Since august - for a month
since 1985 - for 30 years
since Wednesday - for 6 days
since six o'clock - for three hours
since my birthday - for a few months
since I start school - for 10 years
for 40 years - since 1975
for 3 days - since Saturday
for 2 months - since July
for the last two hours - since 6 p.m.
for the last two weeks - since September, 14