Bill, I think that this may have to be a "try it and see" type of thing. Why would a prolonged photoperiod over the course of several weeks specifically pose an algae risk? I can't think of one. Plants and algae are always battling one another while the lights are on, whether they have a dark period or not. Excessive iron and silcates seem to trigger algae issues within a planted aquarium, but sometimes it is too anecdotal to tell if it is excessive or lacking nutrients that can trigger an outbreak. For the terrestrial portion, I would imagine that keeping things a touch drier than normal would eliminate algae from becoming a problem.
The only thing that I can see becoming an issue would be that your CAM-based based plants are going to start to weaken because they ONLY take up CO2 at night. These would things like Tillys and Broms. So, you do run the risk of inadvertently growing some of your plants out like crazy, and seeing others die off inexplicably. So, it wouldn't be any potential algae issue that I would be worried about.
Your best bet, in my opinion, would be to attach a CO2 line into the tank, and just leave it on a very slow flow....maybe 1-2 bubbles/second through the CO2 tubing, day and night, and keep your photoperiod at 14 hours. This would allow for an increased level of CO2, which would benefit the plants. The trick would be to not overdo it....plants need O2 as well for respiration.
Slow and steady, ultimately, is better than fast and furious, IMO!!