to the best of my knowledge... is MBZ/Bosch's designed-in "guestimate" of just how soon you can actually try to successfully crank over the engine... based upon temperature sensors on the engine block and on some models I think there is actually an actual air temperature sensor. Leave it to the Germans to over-engineer such things.

As to the manual up/down-grade old fashioned relay kit, you can find one version by going to www.**************.Com and then use " manual glow plug relay ". His are a bit pricey so you might want top "Google-around" for a better price. I think there is remember a THREAD on this FORUM's WebSite.... hmmmm... here it is:
http://www.peachparts.com/shopforum/showthread.php?t=155464&highlight=%22manual+relay%22

Ain't this FORUM great!!! They get as much of my parts business as "practicable" from now on!

Regards,
Sam