So you don't get a set time, but an hour window. And the system will not let you overlap. So what that means is that even if you have Space at 9-10 and Splash at 10-11, there is no problem getting between those opposite ends of the park, because you can do Space at 9 and Splash at 11.
My strategy, and others will have their own, is to get them as close together as possible, and I stack them in the morning. Because as soon as you tap in for your third, you can book another one. Then as soon as you tap in for that one, you can book another one.
When I first make my fastpasses, I just grab the times available as close to each as possible...(for some headliners they can be difficult to get morning times) I’ll always go back and try to modify the time to shift them closer to one another since they always change in availability over time.
You're booking a one hour long window where you can use the fastpass at any time during that hour (and they'll often give you a few minutes grace period as well if you're nice), not a specific time. So if you book a fastpass for 9-10am, you can show up anywhere during that hour to use it. That means even if your next fastpass is from 10-11, and you don't get to your first one until almost 10, you'll still have almost an hour to make it to the next one before it expires.
I would strongly encourage you to book them back to back, and as early in the day as possible. if the park opens at 9, then booking them 9-10, 10-11, and 11-12 is fantastic if you can do it for the attractions you want. As soon as you've used that last one you can use the app to book another, and keep booking new ones as soon as you've used the last one.