Update on my situation;
At the end of last week I ended up 'crashing', more or less I couldn't get a nap and I couldn't get to bed early because of a change in schedule.
Anyway I fell back into polyphasic sleeping, and now I decided to take a different route in this experiment.
First I will become a early riser (started yesterday) waking up at 5 am everyday for a week or 2. This isn't hard to me at all because I'm still somewhat used to waking up at 5 am because of delivering newspapers for 2 years. The idea is to get to sleep when I am tired and being able to clearly notice that I'm tired in those 2 weeks.
When I am finally used to this completely I switch to biphasic sleep by getting in a extra nap in the evening which should eventually shorten my core sleep. This allows me to get into biphasic sleeping without the adaption phase...