I would say the one hour is plenty. As others have mentioned, the ride is'nt very long, but it is fun! They have baby/kid seats for toddlers too. We did this with our 3 yo daughter last time.
I do not remember if we had a wrist band or not, but we rented them near the main beach and biked near the adult beach, airstrip, etc. The cold water stations were a suprise! We had our water bottles and filled them up at the end of the path. There are two (or more?) bike stations where you can leave your bike, pick another if needed, etc.
I would'nt do the all day unless I was planning to bike a lot or was really slow...or shared with other people, etc.
If you had four adults/older kids that could the two bikes first...then switch off.
LisaCA