Sealing felt roof in cold wet weather

my felt roof has small leak which is allowing water to leak through onto inside of the roof (see picture).

its next to the vent pipe for the tumble dryer and on the top this area of about 50cm x 50 cm has been sealed previously (probably when the vent pipe was installed 20 years ago) with a grey mastic compound and the water is visible directly below this sealed area.

I imagine that one of the sealants e.g. Flexocryl, Isoflex etc would resolve the problem but they all seem to state that it needs to be applied above 5-10 degree C. will this stuff still be ok today at 2-3c?

Also, some of these products have confusing information e.g Flexocryl: " Ensure the roof surface is structurally sound, clean, dry and..." then it says "For wet or dry surfaces" ??

I dont think Isoflex is any use on damp. Acrylpol is ok in slight damp but why not wait until its a bit drier.

ok, so if I avoid wet days and dry the area with a blow torch can I still apply in cold weather?

Also, will the wet-through wood dry out properly?

Can't you put a fan heater in the shed to keep it warm while you do the work.

and a deck chair and a beer

Blowtorch would be a bit brutal, if you can mop up any puddled water then heat the failed bit with a hairdryer, you're less likely to melt that placcie pipe (or set the roof on fire). Acrypol is perfect for that mend, if you do go hairdryer route take care with extension cables (240v in the wet outside can be dangerous, especially up a ladder)

EDIT Yes the wood will dry out once the leak is fixed,