Reception is a good time to invite the whole class and get to know the children and parents. I think afternoon is a good time for 1.5 hours.
If you hire a hall you will need to hire extra time before and after to set up and then to tidy up. You usually need to take rubbish home to dispose of it.
Reception children don't really need entertainment if you can hire a bunch of softly equipment, bouncy castle, bubble machine, have music on the go. The parents will all stay so you don't have to worry about keeping an eye on the children too much. You won't need to bother with party games for 30 children!
Do the food around half-way mark. Feed them picnic type food, cheese puff pastry sticks, sausage rolls, different types of crisps, chopped up peppers etc. Some party rings! If there's a little kitchen bring a kettle, teabags, instant coffee, milk, sugar, maybe some biscuits and let the parents help themselves.
Depends on the school but if they refuse to hand out invites you can give your child all the invites, ask teacher to let them be the first one to leave that day and as everyone else leaves your child can hand out the invites. Make sure you put a note on the invite if you don't want siblings there and give a RSVP date.
Party bags, buy a bulk pack of books and hand each child one on the way out with something sweet like bear yo-yos or a lollipop.