Damp detector - How long for wall to dry out completely

I had a damp problem last year in my bedroom.

Damp was happening because the rain gutter was blocked with leaves and other debris. I had the rain gutter cleaned last April or May.

Last weekend, I bought a damp detector, cost me €15.

The wall is still registering a moderate level of damp.

How long should it take for the wall to completely dry out, I'm hopeing the damp is there from before the problem is solved (and not new damp)

The house is a modern construction from 1986 (cavity breeze blocks on inside, outer layer of red bricks).

Checkout gutters again. Rent a dehumidifer and see how much water you can draw out of wall...Make sure though all windows,vent are closed as dehumidifer will be useless...

I would not have confidence in a damp dector worth €15. One I have cost near to €200. After a year though wall should of been dried out if the problem was solved.