Calculate the difference in access between two dates

i have two fields: TimeFrom and TimeTo
data Type is text.
TimeFrom                   07:15 AM, the format is HH:mm AM
TimeTo                        10:15 AM

(07*60)+15=435
(10*60)+15 AM=615
615-435=180
the difference is        180 minutes
TimeFrom                  10:50 AM
TimeTo                        02:30 PM
(10*60)+50=650
the difference is        220 minutes
((02+12)*60)+30=870                 ' pm needs to add 12
870-650=220
how to calculate the difference in access query, considering time format, AM or PM in single query

select DateFrom,  DateTo ,Duration from tblTable