The sin function takes a value between 0 and 2*pi ( ie. 0 to 6.283 ) ( or multiples thereof ) and returns a value in the range -1 and 1.
'#DWFSS# varies from 0 to 60 once per minute
Therefore, sin (#DWFSS#) will oscillate in the range -1 to 1 just under 10 times per minute ( ie. 60/6.283 )
If you want it to oscillate faster then you would need to multiply #DWFSS# by some number greater than 1 ( eg. sin(#DWFSS#*4) to oscillate 4 times as fast)
And likewise, if you want it to oscillate slower then you would multiply it by a number less than 1.
Pausing at the ends would require something more complicated.
A simple ( but not necessarily very smooth ) way of doing this would be to clamp the output.
So, suppose you want it to rotate +/- 90 degrees. You could set up the sinusoidal part of the expression so that it oscillates through a larger range, say, +/- 150 degrees and then clamp it to +/- 90.
This would produce a rotation that follows the shape of the grey curve in the graph below:
That is, the object would rotate until it reached 90 deg and then remain stationary for a time until it rotated back the other way. The downside of the expression is that the transitions from moving to stationary would be abrupt.
I hope that helps.