This is what I commonly see and it gets the point across... "PICK-UP TIME".
Personally, I love the it. It gives me a firm time frame to schedule around. We have 2-3 hours to play with the little one, go shopping, etc.
For: Sara's 5th birthday
Pick-up time: provide a 1/2 window
Also, some have listed a time for "cake", if they're inviting parents/siblings to join in the fun! HTH!