Edit runtime of created giveaways?

You can write to support to ask them to do that for you(make it urgent if you want to make it end very soon perhaps). You can't edit the giveaway after it's created yourself :)

No way to edit or change it yourself, you could likely try a support ticket but I dont think it'll help much but who knows

Alright, thanks folks! I opened a support ticket, maybe they do me a favour :)

You know, the giveaway page has a confirmation screen SPECIFICALLY WARNING YOU that you cannot change anything about the giveaway once you commit to it (except the description, which you can edit whenever you want, as often as you want) for a reason.

Unless you have a very critical reason (for example, you're in the military and you just got told you're being deployed in two days--I'm guessing they'd have sympathy and help), I think you're not gonna get very far with a ticket. But, it's worth a try. The SG staff are pleasant and helpful.