Maintain Visits on Fixing Date & Time

Is there a way to maintain my visits in PSO when fixing the allocated start date and time?  Example, I have an 8 hour activity.  PSO Splits the activity into 3 visits (All the same scheduling activity ID).  When I fix the date and time in PSO, it fixes all 8 hours to a single visit starting a visit ID 1 ignoring any availabilities set on the activity.