If I use Discipline, does it stay in effect at the end of my turn when Glowstone deals 5 damage to my units?

I couldn't find "Glowstone" in the card database — it doesn't appear in my current index. But I can answer the general timing question about Discipline and end-of-turn damage.

Discipline's +2 Might lasts the entire turn, including into the Ending Phase. The buff expires during the Expiration Step of your turn's Ending Phase (Rule 317.2.d — all "this turn" effects expire simultaneously). Healing also occurs in that same step (317.2.c), before the buffs expire.

So if Glowstone deals its 5 damage during the Ending Step (317.1 — "at the end of the turn" timing) or during the Expiration Step before the "this turn" effects expire, then your unit would still have the +2 Might from Discipline when the damage is dealt, potentially surviving a hit it otherwise wouldn't.

If you can share Glowstone's exact card text, I can pinpoint the exact timing and ruling. It's likely a Location or an effect with a specific trigger phrase like "At the end of your turn" or "During your Ending Phase" — the exact wording determines the ordering.