good idea removing branches in the stagnant bottom.
and central air... where does the water go from the unit? is it located indoors or out? AC lowers the humidity in the rooms it is cooling, and sends the moisture to wherever the heat is going... usually outdoors... i have never heard of one running in the cellar like that, but it's worht looking in to.
oh- and if you want to swap day/ night, an extended dark period is safer than an extended light period. I have done that before with no ill effects, and greenjeans did it when she moved her grow to her new house... just wait for lights out, unplug everything, and adjst your timer... then plug back in when you want 'day' to begin from now on.