Personally, I've never left the lights on during the last 24-48 hours. I've always harvested right after the 12 hour dark period based on advice I've received from other growers. They've mentioned several reasons for this, most notably discussions involving trichomes being at peak level/quantity after dark phases. I've tried one harvest after 36 hours of darkness, can't say I noticed any difference. To be honest I've never looked into the plant biology behind this myself, merely accepting most veterans advice on the subject. I don't imagine that you would experience significant pitfalls after 24 hours of light before harvest, but it certainly doesn't appear to be the ideal method. Please let us know if you decide to try this, love to hear if theres any noticeable differences in final harvest.