Percentile function using time in Access

Question

I'm trying to calculate the 90th percentile of travel time for districts. I'm using MS Access.

SELECT DISTINCT District As District_Num, 
PERCENTILE_CONT(0.9) WITHIN GROUP (ORDER BY Travel_Time) OVER (PARTITION BY District) AS 90th_Percentile
FROM [Incidents-J];

I'm getting the error message:

"Syntax error (missing operator) in query expression 'PERCENTILE_CONT(0.9) WITHIN GROUP (ORDER BY Travel_Time) OVER (PARTITION BY District)'

Note, travel_time is in the format of h:mm:ss. Is this the issue? Is so, what would be a way of converting it into something useful (ex 0:01:20 into 80)?