hes a prize winning scientist.
who had been given a performance enhancer.
Who also happened to collect, and know the meanings behind, several masks.
Is it so radical to think that he made it?
Stromm was found the morning after osborn took the meds. Taking into consideration that the facility was abandoned when stromm and norman did the test, that puts the time around 7-9:00. We see that the actual change in norman only took about 4-5 minutes.
Now, because harry was preparing to go to school when he found his father, we can assume that it was around 7:00 AM to 7:45 am. So, using his extensive background in various sciences and his knowledge of how certain traits in masks effect humans, it isn't such a radical idea to say that norman made it. 10-12 hours would have been plenty of time for norman without the enhancer, and since he took it, that might've shaved off an hour or two. This left him with plenty of time to get dressed, and go to his room.