Example from my own writing:
One time, I sent letters, pretending to be a god.
I spent last week sending letters, pretending to be a god.
The recipient of these letters was Aiko Kobayashi, the girl who sat six rows behind me ...
I just wrote last week because I felt that writing: I sent letters, pretending to be a god was a bit, dunno, just didn't sound right.
It this a bad writing practice? If the time frame is irrelevant, should I use One time, I wrote ... instead?