Oh shit they avoided a time loop nice
From how it went, frieren saw the spell, recited it, then went back in time to discover the passage.
I assumed when she remembered the spell, she told it to himmel and crew so they could scratch the spell onto the monument that she would see in the future, thus creating a time loop.
What actually happened is frieren pointed them into the direction of the time spell, but didn't tell them it directly before she returned to the present, so himmel and crew studied the passage for decades to figure out the spell and avoid the timeloop altogether.