The first level is about 2 minutes long maybe 2:30.
IIRC there is the bit with the steps up and then a bit with steps with an odd rhythm of jump, drop, jump jump, drop, etc... then another bit with boxes and then the end after that.
In total 3 or 4 sections where the floor disappears.
It took me about 650 attempts (in the stats) to complete the first level anbd you can also see you progression through the first level in the stats aswell.