Welcome to Vine. There is a great store of info and advice here and everyone is very friendly if also a little mad.

Initially you probably won't need to water much, due to condensation etc. After that be guided by the condition of the compost and the other environmental factors e.g. how warm your house/window sill is.

The instructions I had suggested filling the trays and allowing the compost to warm overnight before planting so you are not sowing into cold compost if it has been stored outside.

Congrats on your purchase. I love mine. Purely in a platonic sense of course.

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Bright Blessings
Earthbabe
If at first you don't succeed, open a bottle of wine.