The year, engine size and if it is the intake manifold or an exhaust manifold gaskets would help.
5 to 7 depending on experience.
around 6-7 hours according to AllData
It should take about an hour to change the intake manifold gasket. This part can be replaced by taking off the intake manifold cover, cleaning the old gasket off and sealing a new gasket in the space and tightening the bolts. When other things are in the way, like the alternator, it will take longer.
if its a v6 and you take your time. it takes about 6-8 hours, depending on how fast you work !
The labor charge to replace and intake manifold gasket, on a 1999 Chevrolet Tahoe, is approximately $180. It takes approximately 2 1/2 hours to replace the gasket.
I've done several at my shop--these are not easy at all--the 5.5 hours alldata says it pays to replace the intake mani gasket is crazy--it takes all of 10 hours--most likely easier just to pull the cylinder head
you need to take the intake maniflod off, and the 2 screws on the back of the manifold. total time 2.5 hours, replace intake gasket or reseal it...
To be fair: about 4 hours. I charge $240.00 labor to do that job.
5 hours labor Book time. A good experenced mechanic can do it in about 3 hours.
About 2 hours.
Plan on at least 6 hrs.
You should expect to pay between 50 and 80 dollars for the gasket and between 4 and 6 hours for the labor at your shops labor rate.