Rob, I don't think there's any relationship between glowplug condition and the relay's time, but of course, I could be wrong. A couple of years ago, my '84 300D's glowplug relay wouldn't stay on, and I was able to fix it by replacing a bad electrolytic capacitor (100uF, 16v) on the relay's circuit board. An easy, cheap fix and it's been working well since. Don't know if this is the source of your relay's problem, but at least it's something to consider. Good luck.

Jerry