I think depends on context, of course most of times you will see it with a "fairy tale" ring, I mean, these old fair tales of old (and in some novels of today...denoting some old habit or far away time!)    Sometimes, more rare than not, you can see it as:

          a long time ago/long ago - há muito tempo

          there was a time (in wich) - houve um tempo...

          in time/once - em uma época..

     I mean, it has a "feeling" of "some time ago"; but with a sense of being "centuries ago".     Like when you experience a blackout for two hours, it´s not much but you

fell it like too much time (since you miss your dearly comfort taken out).    So, nothing comparable to the slowwww time in fairy tales.