That is very tough to answer, because there is no one answer to this question
Are you using clear cups ? I will be very careful since you have heating mat on which will dry moisture even more quicker. You just stick your finger and feel if it is still moist. You can use water sprayer and just do a little spray instead of giving direct water.
If you post some pictures with some time line like when these were started then we all can take a look and suggest.