My dentist gave me a tube of poladay CP 35% tooth whitening gel with my Invisalign trays. Is bleaching my teeth once a month OK?

35% carbomide peroxide whitening gel is safe for use but I would limit the wear time to about 30 minutes a day to reduce sensitivity.  The Invisalign trays will fit snug so you won't need too much gel in each tooth slot otherwise it will just be wasted and make. sure to wipe off any excess gel from the gum tissue. Once you are satisfied with your tooth shade occasional touch ups are necessary to maintain the color.  Your touch ups may be necessary once every couple weeks or so, everyone is a little different. 

Yes, you can bleach once a month without damaging your teeth as long as you are following proper instructions. Bleaching once a month can remove superficial stains like coffee and tobacco stain.  If you are looking to bleach deep into the tooth and change the color of the tooth, it is best to consistently bleach every day for 2 weeks followed by use of a mineral paste such as MI paste to strengthen the enamel and reduce sensitivity.  If you have sensitive teeth you may need to limit the length of time for each bleach session.