IMPORTANT: Don’t cover pots with plastic wrap, don’t use a humidity dome to seal off the pots, or place pots/rockwool cubes in a propagator that’s completely covered! This prevents fresh air exchange, raises humidity to excess levels, and easily facilitates the spread of fungus. The seeds then rot before they can germinate. Excess humidity coupled with lack of oxygen is the #1 cause for poor germination results!
If you germinate your seeds at room temperature, and have properly watered the substrate, there is no need to be concerned that it will dry out overnight. Only the substrate requires sufficient water for the seeds to germinate - the outside humidity can and should be be low to moderate (i.e. max. 55%). Low humidity in the room does not interfere with germination or healthy seedling growth. Remember: cannabis is not an orchid! Fungal spores are everywhere: in the air, in substrates, ... and they await the conditions to spread and attack organic substances such as seeds or the roots. Common fungal infections are pythium and fusarium. Young seedlings are also prone to such infections because their cell tissue is very soft. Over-watering and/or high humidity trigger such diseases like “damping off” which quickly kills seedlings.