Dark spots are due to previous sun damage - nothing to do with premature tanning in an MT2 cycle.
If you are very white naturally (i.e fitzpatrick type 1) then you should wait at least 3 weeks before getting UV exposure. (3 weeks from day 1, not 3 weeks after loading).
It takes time for the skin to adjust, it's not just a matter of how many mg's of MT2 you've taken. The melanocytes can't expand their branches & fill with melanosomes until skin cells currrently in the basal layer have been replaced. You can't speed this up.
People who tan quickly from MT2 already have type 2 or 3 skin.
0.5mg/ day is plenty ! No need to change. Just wait.