How long does siding and trim need to dry out after days of rainy weather, before it can be painted successfully?
Usually 24 hours is enough to dry out siding. It depends on the amount of humidity and the temperature. If the humidity is high after the rain stops then allow the siding to dry for another day. Same is true for temperature.
If the siding looks and feel wet then wait. If you have sunny warm dry weather, then your house should dry out quickly. The rule of thumb is "less than 15% moisture". This could be checked with a moisture meter.
I put primer on the outside of my house a couple of days ago. I haven't had time to finish painting and it might rain for a day before I can finish. Can I finish painting after it drys up or do I have to add more primer?