I just bought two Trimble DA2s. I want to find out more about Trimble Catalyst On Demand. If the first user has claimed an hour, can the second user use the same hour, or does he have to claim another hour from the pool?
Trimble Catalyst subscriptions are licensed "per user" for use on one device at a time. So in your example each user would claim a separate 'hour' from the pool (and not share the same hour)
We have some specific guidance on how to Use a Catalyst On Demand subscription with the Trimble Mobile Manager app and I'd recommend you take a look at the Trimble Catalyst FAQ's and the Support and Resources section of the Catalyst DA2 product page
Is it possible that unused hours are returned to the pool after being checked out? Let's say I assume I will need about 4 hours to do a job, but I only use 3 hours and close out Terraflex and Mobile Manager. I know you can extend it hour by hour, but I haven't seen or read anything about unused hours that are checked out. Will they return to the pool or are they lost?
No this isn't possible. Once you start (or check out) an OnDemand session it has effectively been consumed will run it's course (1,2,3... hours) then expireThere's no returning unused hours, but you can extend a session at any time so there's no need to guesstimate. Just take what you need on an hourly basis