Visitation Vent

Sigh. A little background: I'm in Tampa, FL (look on the map!), and my ex is in Missouri, about 2 hours south of St Louis. I'm going to fly up to St. Louis on Wednesday the 17th, to drop off 3 year old DS for him to stay w/ her for Christmas, and New Years.
I get a text message this afternoon to tell me that it's really cold, icy, all that stuff, and that maybe DS's grandmother will be the one to pick him up. Ok, no problem. We still haven't established exactly when and how he's getting home: is she going to fly with him, are she are her bf going to drive all the way down here (I don't know why; they say it's cheaper, but really?), what? And when? She won't say, hasn't said, is waiting for her BF's employer to decide if he can have off the day after New Year's Day, which is a Friday. And is still waiting, won't give me an answer because of it.
I've been thinking that 3 weeks is good, as he's handled 3 weeks with her before with no problem back in the summer, and she said she didn't want to travel during her daughter's 9th birthday on Jan 5. I'm off the Friday of that week, so that would give her 3 weeks and 2 days to be with him, and she could fly back w/ him. I've even offered to pay for two of the three tickets that would be required...
So we're texting back and forth. She wants to know if I need to "pin down a day" (uhm, yeah!). She then asks me when I want him back...I thought we had discussed this, but here she is, asking me again. I'm slightly vague on when he should be back because of the birthday of my ex's daughter, and her not being sure of how she's going to bring him back. I know I'm being maybe just a tad too nice, but she's been doing this for a couple of weeks now. It's time to commit to something. (I'm not sure why I'm having a hard time setting a limit w/ her, but I am.) She says, "Name a day, and it's my responsibility to get him there." So I finally say, by Jan 9, at the latest. Then she goes back to the 4th as to when she'll have him back, even though she admits that flying back w/ him on the 9th is "generous"...
Why wouldn't you want to have your kid as long as possible? I'm only going this long because she won't get a chance to have him this long again for 6 months. She'll see him a week or two this spring, either late March or April sometime (around Easter), and then again for 4 weeks this time in the summer in 2009. Ugh.