Fanatical Question

If you input the key right away even when the giveaway ends the person who won the game can't see the key until you click on "Send key".

If you go to the page you bought the bundle from and click each individual game there should be some note right at the top of the game's description telling if it's region restricted (e.g. Blood: One Unit Whole Blood from this bundle, it can't be activated in Germany).

You can also check the threads for the bundles on the Deals forum here on SG, they usually have notes about region locks, if not in the first post usually someone in the comments will mention it.

Personally I put the key in when making the giveaway as usually I have quite a few on the go at the same time. You can enter it yourself after the giveaway has ended and send then and its fine that way too. Whatever you prefer in all honesty.

Restrictions usually is in the top right corner in the box where the key usually is.