We often use for and since when talking about time.
A period is a duration of time, for example: 5 minutes, 2 weeks, 6 years. For
means "from thebeginning
of the period until the end
of the period." For
can be used with all tenses.since
A point is a precise moment in time, for example: 9 o'clock, 1st January, Monday. Since
means "from a point
in the past until now
is normally used with perfect tenses.