My memory recalls 10-15 minutes TOPS---. No weight on the roof, at most a little push downward on the top---basically pushing the seal between the top/bottom, not much more than that. This is total time, pushing in beds, lowering table/stove top, etc.... The actually dropping of the roof. Maybe 5 minutes, depending if someone helped me keep the canvas pushed in.
Remember the top should go up/down with the stabilzers in the stowed position. This means putting up the top prior to deploying the stabilzers. Stowing stabilizer prior to lowering top. The reason for this is "frame torgue". Twisting the unit can but an added strain on the tracking/pillars (whatever they are called) that go up with the top. If the trailer is "sitting" naturally, there is less change of the top binding....At least this is what my old coleman manual taught me.
As far as lowering it SLOWLY. The only purpose I see for a slow lowering is...in order to make sure the canvas is tucked in so it does not protrude beyond the confines of the top/body. In other words...you walk around continually pushing the canvas in, so it does not go between the top/bottom. I would lower 1/4 way...push in canvas. lower again, push in some more. Stop lowering just "UP" enough to get my hands in...make sure the canvas is pushed in...then lower the rest of the way.
If you are having to put a lot of pressure on the top to get it latched...you might want to make sure the canvas is not between the top/bottom.