As with any cleaning task, the length of time it ‘should’ take to clean your bedroom is entirely dependent on the general state it's in. Julianna Poplin, professional declutterer and owner of The Simplicity Habit explained, “How long a tidy takes really depends on how long it's been since it (your bedroom) was last cleaned, and how full the room is."
But if you want to know how to clean your room fast, you'll likely be relieved to know that "most bedrooms can realistically be cleaned in under 20 or 30 minutes, as long as they aren't crammed full of excess stuff," according to Julianna.
The idea of 'dirty' is also pretty subjective. For some, a bedroom may feel dirty after just a few days without cleaning. But if your room for any reason hasn’t been cleaned in a long time – and there’s lots of built-up dust or dirt – it will of course take longer for it to be returned to a clean state; likely a couple of hours, at the least.