I did notice after 10 to 20 minutes my scope would start drifting off band and I would have to readjust the ethlons. I have a Lunt DS 100mm pressure tuned scope and am wondering if I need to replace the O rings in the ethlons (the scope is new to me, but is ~4 1/2 years old) or if the band drift is due to something else I've not considered?
The blocking filter temperature change will not affect the etalon CWL, but may make the image dimmer as the BF cools significantly and the BF CWL shifts blueward and the transmission of the etalon is dimmed. This could be what you're seeing. Warm the BF up with a dew heater or other, and see what happens.
I you get actual etalon "drift" off-band, you either have a pressure leak O-ring issue, or the etalon temperature and spacer thicknesses are changing, and you have to re-tune the etalon to account for this etalon gap thickness change. Air temperature and barometric pressure changes can also affect the etalon CWL, and it might ultimately be difficult to differentiate what is going on. But in the end, etalons do sometimes need slight tuning adjustments.