I was posting back to you, when Appliance Guy offered an answer, so I'll retype the post.
He's correct in saying that the glow coil could be causing the problem, but there's a couple of things that should be checked before you buy one, as they don't come cheap.
First, check to make sure the burner orifice is not restricting the gas flow. It could be partially clogged with grease. It's not all that easy to remove the burner, because there's a very limited space to work, but it's worth it if it saves buying a new glow coil. Tip: If you have trouble removing the burner, look at the back end of it to see if the shipping tie down wire is still there.
Second, try to wiggle the coil to see if the hold down screws have rusted at the floor pan and come loose. It does'nt take much movement to interfere with the light off time.
If these two inspections check out OK, it's time to buy a new glow coil. I'll post back with a part number and a price.