Like GW said above, you don’t try combinations it’s just done by feel.
It’s all down to how much play there is in the mechanism, to crack a very cheap one you just pull on both ends whilst turning the combination, one wheel at a time starting from the first combination barrel. On the cheap ones there is enough play that it will jump into place when you hit the right number (when pulling on both ends of the lock), it does take as long as how quick you can turn the barrels (secounds). The better quality ones take much longer as you have to be able to tell the slight difference in feel when you hit the right number. Either way it’s easyest to do it “blind” as you can concentrate on the feel more.
If you are concerned about bike security then buy a sold secure rated d-lock or heavy chain. Not a cable or combi lock.
No i’m not a bike thief, but we do like to test new locks at work.