It just depends on what you want to do.
The families with kids tend to be around from 4 - 9 pm. They like to collect candy, see the characters and they usually stay for the 1st parade. You could maximise time on rides; if the wait times are low.
There are some characters that are just not usually available for
MNSSHP. Especially the 7 dwarves. So, if you want to meet them, line up early. And I mean early. The queue for the dwarves can get massive.
I found that most of the adults that dressed up were very happy to have their picture taken, if you asked nicely. Crowd watching was something that was an unexpected pleasure as the costumes were just so good.
If you decide to see the 1st parade, then you might want to pick your spot early and mark out territory. If you choose to be at main street or the hub, people start marking out spots at least 90 minutes beforehand. But most of these people stay for the parade AND the fireworks. So, depending on where you want to see the fireworks, you might have to mark out a spot.
It is easier to find a spot for the second parade; but again around the Hub and Main Street is busy.
Check out the map for where the candy spots are. There will be a couple of places where there will be clusters of candy barrels. Those will be good places to hit later in the night to collect candy. The CM are usually a little bit more generous with their handfuls closer towards the end.
It was definitely easier to get on rides later in the night....but sadly, not for Peter Pan nor Dumbo. PoTC was walk on, as was Space as was Buzz Lightyear.
Have fun!