Let’s go over how not to lose your Stars. (No promise made about your marbles.)
When sending characters on Star earning tasks, make sure that the total adds up only to what is required for the level. Anything more will be lost.
Say, for example, you have 5 characters (1 premium) working on a level requiring 30 Stars. That’s 6 Stars for each 3 hour round. It will take 3 rounds to complete the level. Only 3 rounds because of the extra 5 Stars earned from the Space Training Station, also every 3 hours.
Now, that total will be 33 stars. You will be losing out on 3 stars that will not apply to the next level. The levels are always zeroed out.
So, in this example, simply delay collection on 3 characters’ tasks. Offset their job by 10 or 20 minutes (or whatever you’re sure you can get back to before that job is ready). Once the next level is ready you can collect those 3 Stars and send all the characters on their next 3 hour round.
The main benefit in watching the counts is to be able to send the unneeded characters on others tasks, such as to make money.