You're welcome! The best guideline I've seen for low level advancement for OSE remains Tom Moldvay's advice in the back of 1981 B/X that if no one has hit 2nd level within 3-4 sessions, you're probably giving too little treasure.
The old school game I ran from 2020-2023 maintained a pace of about 3-4 sessions per level on average for the first couple of levels, then slowed a bit, then slowed even more after level 5. But by level 3 characters are a bit more durable and capable, and level 4 is a big one for most of the classes in terms of combat, saving throw, and spell advancements, so slowing after that is usually fine, because you're into the "sweet spot" in terms of levels for fun play.