Should I keep vdp the same at night time as it is in daytime
Search the community site for Pete’s response.
My interpretation, assuming that “night time” means that you’re shutting off the lights, there’s no need to follow VPD guidelines but don’t go overboard.
Pete said it better. 
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Here is the thread @OC_Grower is referencing: VPD night settings
This is a somewhat controversial topic amongst growers, but as Pete explains it, both sides are right. VPD does matter at night, just not enough to be optimized for.
This is a somewhat controversial topic amongst growers, but as Pete explains it, both sides are right. VPD does matter at night, just not enough to be optimized for.
It’s my understanding that while the above is true, it’s also my understanding that powdery mildew is a vicious beast and avoiding too much humidity in flower is still ideal.
As long as you have good air flow at top and bottom of canopy, PM shouldn’t be an issue. 85% of my grow I was at 50-55% RH with no issues whatsoever.
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There are strains that are naturally resistant to PM, so your results may not reflect what they can expect depending if that was a factor for you or not.
I second Growmodrobro. Breeders these days seem to have mostly abandoned seeking disease resistance, but occasionally you’ll grow a plant that just can’t get powdery mildew.
I found a strain like that recently and I’m planning on using it as the male for my own breeding and I don’t plan on keeping a single offspring that ever shows PM. I didn’t realize that PM was a choice that people were just accepting for the most part.
50-55% is also arguably too dry to get the best results (“they say”) if you are supplementing CO2 and using high intensity lights, unless we’re talking about late flower or cool temps.