I majored in Child Development and taught preschool for 3 years before having my son.... and can't wait to get back to the classroom!! My classes were 3 hours long and the children had "free play" for 45 minutes. The next 5 minutes were clean-up time. Based on many modern studies and theories, children can never play enough!
Really, it is the quality of the play, not the quantity. If you notice that the teachers interact and help guide play with the children, 50 is not too long. If the teachers sit around and only interact when there are incidents, then even 10 minutes is too long!!
It is interesting that there isn't more consistency between the classrooms - does the 50 minute free play classroom have any group time? (really, even group time can be unnecessary if the teachers are well engaged and include all aspects in their class guidance)
ALSO, it depends on the age range of the class... if the children are all on the younger side, 2-3, they are a little young to be sitting for very long and they actually need more play time in order to hone their social skills.
However much you don't like the longer free play, it may not be a good idea to arrive late - as a teacher, I have watched children come in and not be able to transition well into a classroom of already playing children. Even if it looks like your daughter can transition well into the room, other children may struggle with a late comer.
Free play has much more to do with the developmental aspects of socialization and less to do with academics. I think it's great, though, that she has two groups to go to - each sounds like it is offering enough different developmental activities.
Think of play as a child's way of working on social boundaries.
All of that said, I wonder about asking the 50 minute free play classroom about their circle time. Ask if they have a curriculum for circle time and if so, how long do they spend on each topic? Ask them if they have songs that they open and close circle time with to help the children get into a routine. Find out if you can volunteer to read a book during circle time (I LOVED it when parents came in un-prompted to read or sing with the kids!!).
Good luck!