I suspect you're not translating this right. "Qui" means "who", not "when".

From here, the words seem to me:

T'en souvient-il ? tous les jours étaient beaux.

Qui me rendra ce temps prospère?

"Do you remember? All the days were beautiful. Who will bring these prosperous times back to me?"

(Your quote is almost identical, except you use "nous", we, instead of "me", me, and you drop the important closing question mark.)

Great article in general. It's something of a mystery to me how we have essentially forgotten so many styles of music even though we have complete records of them. Hope your concert went well!