5 hours today for my heritage grande to start
I think you're on the right track as long as the bulb fits without touching the globe, I think 1/4 is the proper distance. A regular 100 watt bulb will not work as well as a R20, neither will a lower wattage R20. I have tried both ;)
Room temp says 75 degrees. Feels cooler than that in here. Maybe is just the weather, but my other grande acts normal. Will try a bulb extender this weekend and then try other options like a R25 or 125w R30 used for reptiles to get more focus and heat going. I don't think I should try a normal sized light bulb because they're not a focused light, but might be an option to try.
My heritage and rainbow grandes both take about 6-7 hrs to get going. My Grande from back in 2002 takes about 4. I think the difference is the holes in the base on the heritage ones. I haven't tried the rainbow one in a solid base yet to see if its any quicker.
I had a bulb extender on the old Grande awhile ago before I switched to the heritage bases. A word of caution: if you do that be VERY CERTAIN that the bulb is NOT touching the bottom of the globe. If it is...there is a strong chance the globe will crack. I used some putty on top of the bulb in a small ball to confirm it was not touching. You need an air gap between the 2. That being said...the extender will shorten warm up times, but I found that I'd then have to dim it down some once it got going.
i agree with trying a bulb extender. the bulb needs to be very close to the bottom of the globe, else it won't heat properly or will take many hours to do so. this is especially true as the weather gets cooler. one of my heritage grandes would only produce small globes until i added a bulb extender. now it flows just fine.
Even my 52 oz'ers take longer to heat up in the cooler temps so I could imagine a grande would be tough.