Room temp is fine during lager yeast culturing.
I"m just about to begin lager starters (one stir plate, one jar) from harvested 2124 slurry. It's all on my kitchen counter. After 24 hours, I'll crash both to 35*F until Tuesday. Just before pitching, I'll decant and let them warm enough so that they are fairly closely matched to the 48*F wort I'll pitch them on.
Good Temp Control -----> Happy Yeast ------> Tasty Brew