I did a Marmalade and Mustard glaze the other day. Give it as long as you would for a honey or sugar glaze (it caramelises, and will burn if left too long). Mix English mustard powder with marmalade for a smearing texture. It will soften and run as it heats so should be mixed thick, and put something in the pan to catch what runs off, or it will burn.
I simmered it first with onions and roots, so the oven was only to cook the glaze on.