Is 'μια φορά' equivalent to both meanings: 1) once = one time 2) once = at some time in the past: "Once upon a time, a very long time ago now, about last Friday, Winnie-the-Pooh lived in a forest all by himself under the name of Sanders." - Winnie-the-Pooh by A. A. Milne, E. H. Shepard.
Φορά is not the verb "wear" here. It is a noun meaning "time (with the meaning of instance or occurence)". So μία φορά=one time=once, δύο φορές=two times=twice etc. I'll add the hint so that there is no confusion.