Cutting of the light source does influencing the time it would take, but not in the way you are thinking. "Starting over" is not the way photon-driven (or any, really) reactions - which are just ensembles of quantum events - work.
You can think of it like any other gambling process. Let's say you are in Vegas and you are doing slot machines, where the probability of winning the jackpot is (say) 1/1,000,000 for every pull of the lever. You do this from 10 AM to 12:00 PM and a friend comes by and says, "Hey, do you want to get some lunch?" If you agree to go to lunch, this doesn't cause you to "start over" when you come back, because every pull of the lever has the same chance of being a winner. On the other hand, if you had the time (and money) to use the machine continuously as long as the casino is open, it would be appropriate to say that, on average, it will take you a longer absolute amount of time on average to become a winner if the casino closes 8 hours every night, because you lose 8 hours every 24 hour period of lever-pulling-time. But, if you were to calculate the average number of playing hours it takes to win, it makes no difference if there are casino-closings or not. I.e., it's the number of pulls of the lever per playing time that makes the difference. Needless to say, if you could increase the number of machines you could play at one time, or rig the system to make it more likely that any given pull results in a winner, you can reduce the amount of time it takes to become a millionaire. In the chemistry world, these two things are akin to increasing the energy (temperature, light intensity) or applying a catalyst.