Well, it is not a real sauna, it is a sweat chamber. I took more pictures to show... they break a sweat, the close up look roots, but is actually sweating.
I don't have grow lights, nor I keep my house too warm - it is an old home and leaks heat, don't want to warm up the outdoors, so I keep my house at 65-68- but right at the vent, the forced air is warmer, that is where I put the plastic tubs...
here the lower tub has the cuttings, notice the moist inside? the others above have cuttings in all sorts of stages so, I leave the lid cracked open!
One week of this helps. It must be difficult to put roots, they sweat a lot before... to creat the callouses.
At night time, I throw a towel over the shelf and containers...so it gets warm in there... the forced warm air is trapped for them.