I'd still skip the windowsill during the day. Plants take weeks, months, and some, even years to acclimate to lower humidity. Your confusing the poor little guy. Imagine taking a damp sponge and putting it on your windowsill for few hours. It's gonna dry out. Your doing the same thing to your plant. It's basically getting dehydrated for the couple hours it's out, then re-hydrated when it goes back. Plants develop a wax like coating when grown in lower humidity to protect it from drying out fast. This is why people use the bagging method when they get fresh plants, particularly fresh from tissue culture. It gives them a chance to adjust and acclimate. I just received a macrophylla from AW. I am using the bag method to acclimate it from whatever AW's conditions are to my terrarium which has a RH of 70-75%. Larger plants make adjustments quicker and with less effect, but these small TC plants need time to adjust. My AW hamata clone 1, just started to really grow after 1 year and 3 months. For that time it simply maintained. Also, for a plant to go from lights to sun can result in sun burn, but there is no evidence of that on your plant. Like the others have said, it looks good, but for the long haul, consistency is key.