Calculate time elapsed or worked during (eg) 12:01am to 6:00am

I'm trying to calculate the time worked between 12:00am to 6:00am (early morning).

My data is simply from a data log (for an over the road {OTR} truck driver). What makes it a bit complicated is OTR drivers can work any time period during 24 hour period:
Examples:
A2 04/02/2016 22:10 ON (where A2 contains date+ time in the cell)
A3 04/03/2016 08:10 Off
A4 04/03/2016 20:00 ON
A5 04/04/2016 03:00 Off

Between A2 & A3 the driver worked 10 hours; 6 hours during early morning
Between A4 & A5 he driver worked 7 hours; 3 hours during early morning

Hours worked is simple subtraction but I've run into problems (cranial limitations!!) on solving the early morning calculation. Any suggestions?
Thanks

With A2 is ON time, A3 is OFF time

Hours within 0-6:00 AM:

=MIN(INT(A3)+6/24,A3)-MAX(INT(A3),A2)