I've met you and your dd and she is a credit to you.
You and your daughter know that parenting and being a mum (or dad) is much more than just a few hours on a Satruday or Sunday.
Continue to be helpful about the time that they do spend together - but make him take responsibility for it. It is not up to you to chase him. If he is late - then it is his fault. Make sure that you are doing nice things with your daughter while you are waiting - and try to be nice about the times he is late. You are right not to bad mouth him in front of her - it will only back fire in the long run. (You never know, he might one day get his act together, and you don't want to have damaged her relationship with him, even if it is too late for the two of you).
It may be that the contact dwindles - but make it clear to him that if that happens, it is his reposnbility - that you are not, and have no intention of, doing anything to hinder is access.
It may even be worth (even if you have to smile through gritted teeth) letting his family know that "these" are the times that he has agreed to see his daughter and that you would appreciate their help in ensuring that she is not disappointed and that he picks her up when he says he's going to (and also doesn't cancel). Actually, I'm being a wee bit sneaky there - by "involving" them in that way, if they then at a later date complain that their darling son doesn't see enough of his daughter/they don't see enough of thier grandaughter, you can then smile sweetly and say that you had asked for thier help in ensuring that he did see her!
Anyway, remember you are a good mum! And you have a lovely daughter!