I once placed a can of beer in the freezer for an hour. It did not freeze, and it was great.  However, now I need to cool some whipped cream (un-whipped), and the packet says I need to keep it in the fridge for 24h. But I don't have that long; and I'm worried that keeping it for 1h might be too long.  Is there a rule of thumb (perhaps in relation to weight), or do you have experience with how long I should keep this in the freezer? 
Not the answer you expect.  Cream freezes at 31.5 F.  Put it in a covered bowl and float it in ice water.   Better yet a cooler with ice water you can close.   Not only do you have an optimal temperature but liquid versus air heat transfer is like 100:1.  Liquid density is like 1000:1.  You can drop a beer can in ice water and have a cool refreshment in 10 minutes.  If you insists on fridge / freezer I would do 1 hr rotation fridge (first) then freezer until you get what works.  Maybe like 4-6 hours. 