U got PM bro...
Wanted to trek it but too bad...the timing doesnt fit me right...JYI, u have to start your journey from Jogja town at 12am... yes, 12am... reaching the Mt Merapi starting point about 1am...then start to trek up to the summit and u need about 4-5 hour...depend on the guide who led you...by that time, u will able to watch the sunrise at 5:30-5:45am...

Sorry to tell u...i am too tred to make it to the top..so i skip this part... i only went for the Mt Merapi tour with those scrambler bike...it was fun too...and dangerous!!