I have had to operate fairly long distance with co-parenting with my ex. We are 1600 miles from my SS so that is always with flights.

My exH and I have always communicated from the road if one of us hit major traffic. Otherwise we expect eachother to be where we are supposed to be within 15 mins. 

We dealt with that as well.  By the 2nd year of me living with DH and constantly having to change my weekend plans because she was having "Sunday Funday", I put my foot down.

Agreement was 6 pm on Sundays so the SS's had time to wind down, do homework, eat dinner and be in bed at a decent hour.  Then it was 7 or 8 and summer almost as late as 10.  I told DH that I would just stop being here on weekends and he could deal with it. He told her it would be 6 per agreement or go to court.  She wanted us to just drop the boys off and when she got home, she got home.  They were 10 and 6!  

So DH then changed the location of drop off to the police station around the corner from her.  From then on, unless in summer or holidays if they wanted to stay with us, her mother or husband would be there at 6.  She was usually drunk by 3

We never allowed BM this level of flexibility, unless there was an emergency or an extenuating circumstance where flexibility was needed. Our CO stated 3:00 p.m. exchange times and we stuck to that 100%. We are long distance so we understand some flexibility may be needed for car accidents, weather delays, etc. but that was always communicated and adjusted accordingly. 

Your DH needs to set a time and stick with it. No more flexibility or "after dinner" nonsense. 

My SO's BM is/was like this. They do daily exchanges when it is her custody week (SS gets off the bus at SO's house.) For now, SS17 "manages" his mother, including the daily multiple phone calls and texts to find out what time/where SS11 needs to be dropped off. Prior to this, it was a mess. Never knowing how many people were eating supper, supper usually interrupted by the calls/texts/her showing up, couldn't have any kind of after school routine since she would show up anywhere from 4-10, and sometimes failed to show at all. She would also regularly send others to the house to pick him up, such as her friend or SO, without letting anyone know.

SS17 may be going away to college next year so won't be around to help (and good for him, he's put in enough time as her beck and call.) And having SO bring SS at a certain time doesn't work because this b doesn't keep a schedule like normal people. Runs the roads all day and night.

Idk what will happen next year. I don't live with SO yet, though, since he doesn't know what will happen either. I won't live in a house where that woman has the ability to ruin half the days, though. She has been a little better since they have an open court case, in that at least the overnights with the youngest are consistent. Threats to her CS are all that seem to faze her. Maybe that will help in your case? 

She's taking the proverbial, set a time and stick to it, unless there's an emergency.

We have ss here alternating weekend days on a strictly 10am 6pm rota. Because dd has activities too, the last few times bm tried to mess us around last minute, she was waiting on our doorstep with him or having to go home and come back etc.

I'd make it known you're not available until 7, and if you have to, that you won't be answering the phone or the door after 8pm. Until she gets the message 

I get that it can be hard to hit a precise target.... but maybe it would be good to set a range parameter?  6-8?  and then stick to THAT.  

Unfortunately, sometimes in these cases, you have to just stick to the CO if the other party takes advantage.

Perhaps he needs to wave that stick about.

BM, I know that it can be difficult to hit the exact switch time everytime, but unfortunately, we can't keep going forward with getting the kids hours after the set time of Xpm.  I have been really flexible in the past, but that isn't working any longer, so I need you to make a better effort to stick to the actual time in the order going forward.  Of course, extenuating circumstances or specific plans made days in advance may be considered, but I expect that the status quo and notmal will be that the kids arrive on schedule and not hours later. ok?

and not good ones.

Have a set time and stick with it. Unless emergencies or dire circumstances . Mind you the exes BM always had a dire circumstance on why she was late. I mean late by several hours with no call or text. Her phone always died, or she forgot her phone. Of course it didnt matter that she dropped off a 12 year old at 11 pm on a sunday. She didnt see a problem with that. SMH

When you give an inch these wenches can take a mile. Many a sunday was ruined, many weekends were changed because BM reigns supreme. 

With my kids, for the first 7 years or so, transfer was done at daycare. When they got older, we lived close enough so that they could ride a bus to school from either house, so they would just get off the bus at the house they were supposed to be at. There may have been a few summers or holidays that daycare didn't apply, but then my son was driving and he brought his sister. There was one instance where there was an issue, and it was that my daughter would forget things and i would drive her over to get them. It was cramping my ex's style and he complained, so i stopped. I was tired of doing it anyway.

My SO has a much bigger problem with BM2. This woman does not keep a schedule like a normal person and is out "running the roads" all day. She is not home at any set times and goes different places each day, visiting people, shopping, or dining out, so having SO bring them was never an option. Multiple texts and phone calls every day, just figuring out who was supposed to be where, everything depending on the whims of a squirrel-brained idiot, who definitely took advantage.

For now, SS17 "manages" her and does all the running around and takes the texts and phone calls. And SO is the aftercare on her days so it's a daily exchange half the time. I have suggested that he hold her to a schedule or take her back to court, stating that if she can't care for SS11 50/50, she only get every other weekend, but he won't do that. I think she will do what it takes to keep child support, but i understand not "rocking the boat." It sucks that he had kids with someone like that. I dated a guy with kids before and the BM lived like normal people, so there was a schedule.

ETA replied twice, didn't think first went through. 

If there is no structure  there is no control.  No control and you have manipulation.  
 

We had to spank the opposition with the CO and a Judge a few times over the years when they got creative with sending the kid home on time from SpermLand visitation.