Rating Newest Oldest. Best Answer: Lasagna usually takes about 1 to 1-1/2 hour to cook even in a glass pan and usually that's at 350 - 375 degrees. Start it at the higher temp for the first 30 minutes, then bring it down to the lower for the last half hour or so.ating Newest Oldest. Best Answer: Lasagna usually takes about 1 to 1-1/2 hour to cook even in a glass pan and usually that's at 350 - 375 degrees. Start it at the higher temp for the first 30 minutes, then bring it down to the lower for the last half hour or so.