Sandbox Use and Autoreturn Time

I want to use a sandbox for a build I have but don't want to get stuck having my stuff returned unexpectedly..........The one sandbox told me to turn on "Land Tips" and it would tell me how much time I have before autoreturn...........I get a grey box with info but nothing saying how long before autoreturn.......Can anyone tell me what I'm doing wrong?
Thank You

Click on the bar at the top of your screen where the land name is displayed. In the dialog box that shows up go to the objects tab. Return time will be a number there. It is the amount of time in minutes after an object is created before it will be returned.

I was in one sandbox recently that cleared at set times, rather than a certain number of hours after rezzing an object. Can't remember which, but I'd only rezzed something for a few minutes and the whole sandbox began to clear.
Luckily I hadn't done any work so was able to re-rez the object straight away. I think this was one of the main LL sandboxes, not certain though.

i think this sandbox is removing everything at a set time to.......it says to look at "land tips" by mousing over the ground........i get some info, but no time...........the owner gave me permission to rez a really big build there, so i need to figure out when i'll loose my stuff..........i didn't want to bug the owner again asking questions.