How long do you validate an idea before moving on to a new one?

Could you elaborate a bit more on the state of the idea, eg.:
1. It's a raw idea that needs to be validated (from nothing to being sure that there's something to it or people don't need it)?
2. It's an MVP struggling to get traction and you're thinking about ditching it?

It's more a general question. How people validate their Ideas / MVPs and when they move on to new ones.

For me personally it varies and is based on the specific type of an idea.
Sometimes I just hack up a teaser/landing page outlining the main concepts and start to collect emails and/or Facebook Page/Instagram follows. The rate of signups allows me to decide if I should abandon it altogether, introduce changes to my initial idea & teaser site or forget about the outside world and start to code. For the main part I like to give myself around 2-4 weeks for a soft research (core concept, competition, monetisation) and gathering results before jumping straight to coding.