I'm just created my first giveaway, what would be a good "time range" in your opinion?

If you want my opinion, 1 day is good, then every timezone gets a shot at entering.
Unless it's for some special event, then match the duration to the event.

I've seen people doing giveaways for an hour or so with very good games! Since entry numbers don't matter, at least from what I know, it doesn't really matter. Depending on how much people you want to reach the duration should be longer but everything from 1 hour to 4 weeks is okay. It really doesn't matter to me.