That's actually a bit warm. I lager at 34 degrees, as close to freezing as I can without risking freezing, for one week for every 8-10 points of OG. So, for a 1.064 beer I'd lager for 8 weeks.
I just had a thought- lagers ferment at about 50 degrees. Lagering is "cold storing" after fermentation is finished. We all assumed you meant lagering temperatures, but fermentation temperature should be around 48-52 degrees. If you're talking about lagering fermentation temperatures, 41 is too cold. It's too warm for lagering, and too cold for fermenting.