And by "take shots" you are not doing anything but getting a feel for that level before you step in. It's like checking the water with your toe before putting your bathing suit on.
Taking shots is more about taking a risk in order to move up stakes. So you'd do something like take a shot at 30 buy ins and move down if you drop 5 buy ins at your new level (25 buy ins - so a 30/25 shot). And since it is rather easy to lose 5 buy ins in the grand scheme of things, especially at a level you aren't used to, taking a shot like this is a risk. Ie. if you run bad you will probably fail.
Contrast this to taking a slower approach, where you might say move up at 40 buy ins and move down if you drop to 30 buy ins. This gives you 10 buy ins and enables you to handle alot wider variance.
You can take a shot whenever you like - you don't really need a certain amount of hands. It is more about how comfortable you feel at those levels and how many buy ins you are willing to risk in order to move up quicker.