timestamp + 6hours

If my shift times are 9:00 till 17:00 hr and I need to work 6 hours on this help, how to count the time futher to the next day?

A1
01-01-01-2014 12:00:00  
=B1+"6:00"

this gives
01-01-01-2014 18:00:00

Since I quit at 17:00 i need to work 1 hour left the next day.
Output must be:

01-01-01-2014 12:00:00
=B1+"6:00"
02-01-01-2014 10:00:00

Try this:

Formula:

=B1+TIME(6,0,0)

and change the cell formats

I think I need an If check but don't know well how to implement it.
Something like: hour = +6 and time is <17:00 hr then >nextday + timeleft

Its gives me the right value:
01-01-01-2014 12:00:00
=B1+"6:00"
Result: 01-01-01-2014 18:00:00

But since the I quit @ 17:00 i have one hour left the next day.

Anyone with some input? How can I work this out?
I would like to stop the time at the end @ 17:00 o'clock and paste it trough to the next working day.