[Idiom] only a very short time

[englishhobby]

Is there an idiom for "only a very short time" that could be used to comment on the behaviour of an ambitious person who has just started working in a place and trying to change a lot of things? (In my language you can say the same using an idiom.)

Example: You have been here (only a very short time), you can't critisize everyone here.

Is "for 30 seconds" an appropriate equivalent?

 

[Rover_KE]

I'd say

You've only been here five minutes; you can't criticise (BE spelling) everyone here.