If you want to keep it formulaic and relatively low-level, I'd go with a metaphor instead of being litteral.
The simplest way is to just change it slightly, casting it for Sun duration, at night, like "Your beauty will outshine the stars above, for a whole, magical, night."
Then, you could just use Moon duration. Few candles will last that long, I guess.
Last, I believe you could use a non-standard RDT, the question being what's the closest duration chosen. If the troupe agrees with Fire, you're probably good, at the cost of 1 more magnitude. If they settle on Until, you're toast.