Thank youI installed 2 x sun roofs in my van, whilst on holiday in UK.
Working on my mum's drive, limited tools (my dad's, who died 13 years ago).
Took me around 3 hours to fit both....one over drivers section, one in the centre (between ribs).
Centre one has a VERY slight drip at one corner (glass to frame), but only when going through a pressure car wash....never leaked with 2 feet of snow on the roof!
I'm sure if you just want an opening "vent", should take about an hour to fit using a drill/jig-saw/silicone.
Only thing to watch out for, is the wiring to the roof lights....you don't want to cut through those!
Otherwise, I did both with the roof linings IN....just used a long jig saw blade from outside and cut metal and interior in one go.
Quality tape on the body stops the saw scratching the paint.