Day 43 (from planting), Seedling #1 aka "Frank"
I had intended to wait a few more days before providing another update. However, I have been monitoring some paling at the tips of Frank's first true leaf set. The tips have now browned. So far the damage is very limited and I intend to monitor closely. But I felt this was of enough interest to justify an update. (Dot thus far seems unaffected and I will wait until next update to provide new pictures of her)
My research indicates the browning leaf tips could have a number of causes such as low humidity, overwatering, and overfertilization. There could be other causes as well. Since the seedlings are still in their humidity dome and humidity has averaged 75-80%, I assume low humidity is not an issue. The soil is Happy Frog and I have not yet added any nutrients, watering with distilled water only. Although Happy Frog contains some light nutrients, I doubt they are the cause of the brown leaf tips.
For now I am leaning towards this being a case of overwatering. I have been a bit paranoid about allowing my seedlings to dry out too much, given their fragile state and small size. I may have allowed this worry to push me towards watering too frequently. As an additional data point, I noticed that Frank had recently put out a new root just above the soil surface. It is my understanding that Salvia can do this in reaction to the roots not getting enough oxygen (due to overwatering).
I plan to pay close attention to the seedlings at this stage and monitor for signs of becoming thirsty before I water them further. Perhaps I should have done this all along, as I have with other types of plants. Like I said, with Salvia seedlings being so small, it is possible I employed a heavy (and wet) hand out of paranoia.