Castrum may be shorter than Praetorium, but the player is far more engaged during it. I think it and Praetorium having about equal experience would be fine.

Castrum: shorter, but has far more engagement and player input required
Praetorium: less engagement, but lasts slightly longer

I personally hate getting Castrum over Praetorium. I have to actually do “more” work (e.g., input more into things like mob killing and touching those damned search lights) for less reward. And the time difference doesn’t justify it really.