On my second placement (which is more representative of average school days) I was in a reception class.
I generally got there at about 8.10 and left any time between 4 and 5, some teachers would do longer hours than that and others might do shorter it depends on what they'd rather do at home and what they'd prefer to do at school.
The day would begin by welcoming children into the classroom, changing reading books and taking the register. Then in the class that I was in they split into groups to do different adult directed activities, these would be lead by the teacher, learning support assistants (LSAs) and parent helper, there would also be one group doing an 'independent job'. The groups were of between 4-8 children and the activities lasted around 40 minutes, depending on the children's attention. After this there would be playtime where the children went out and if not on playground duty the teacher would sit with the LSAs have a cup of tea and have a chat (sometimes school related sometimes not) After this the children would return and the same set up as was described before would repeat. Lunchtime- preparation time for teacher and LSAs before lunch in the staffroom. After lunch, same lesson set up as before. Afternoon playtime then after that story time then home time for the children. After this the teacher would stay, tidy up from the day and do paperwork and preparation.
Of course teachers are allowed time for planning inside school hours but it isn't nearly enough and work does need to be done at home. It was taking me quite a while to plan just one lesson but it's something that gets easier with practice (or so I've been promised!).