req_StartTime = input.Date_Field;
req_Duration = 90;
bool_doubleBooked=false;
for each thisRecord in allRecords
{
	thisRecord_StartTime = thisRecord.req_StartTime ;
	thisRecord_EndTime = thisRecord.req_StartTime.addMinutes(req_Duration);
	if(v_StartDate = thisRecord_StartTime)||(v_StartDate = thisRecord_EndTime)
	{
		doubleBooked=true;
	}
}

1.  req_StartTime = input.Date_Field; 
2.  req_Duration = 90; 
3.  bool_doubleBooked=false; 
4.  for each thisRecord in allRecords 
5.  { 
6.      thisRecord_StartTime = thisRecord.req_StartTime ; 
7.      thisRecord_EndTime = thisRecord.req_StartTime.addMinutes(req_Duration); 
8.      if(v_StartDate = thisRecord_StartTime)||(v_StartDate = thisRecord_EndTime) 
9.      { 
10.          doubleBooked=true; 
11.      } 
12.  }