you can read this article below about timescales.
They quote 3-4 hours but the problem is that they do not say at what level the base detection rate is set at....
Certainly for the UK drug driving limit of 2ug/ml it is quite possible to fail 24 hours after smoking a decent joint.
I would imagine that DVLA operate a similar very low threshold or even lower as all they want to find is that cannabis has been used, not that there is any significant amount.
I would guess at 3 days tops for blood, but as the article says, 30 even 35 days for a heavy user with urine.
The body processes marijuana at varying rates, which may change depending on dose, hydration, body fat percentage, and, sometimes, the sensitivity of the test. Learn more here.
www.medicalnewstoday.com