Always On (Closed, Loaded) Temporary Timed Off Switch
What you probably want is a spring wound timer switch with SPDT (single pole double throw) contacts to install in place of the ordinary light switch that now controls your outdoor motion lights.  These are available with timers spanning up to 12 hours.  The SPST variety of this switch is the most common and can only switch something ON for a timed interval, but the SPDT variety can either switch something ON or OFF, depending on the leads connected to the load.

One example would be the 2 hour timer by Intermatic, model FD32HW (I am not recommending this particular product.  It is just an example.):



Be careful when ordering because the SPST variety of this timer is by far the most common.