Translation for 'Once'

I've been working on translating one of my favorite quotes, "Once more unto the breach, dear friends, once more." I've figured out a bunch of it, but I've hit a roadblock in translating "Once". The notes that come with the translation(I'm a beginner in Dovahzul, so I use the translator alot) indicate that it is not the proper translation I'm looking for. It says that "ont" is used to indicate something that happened in the past, so what might I use as a suitable substitute? 

Category: Translation