If it was my app, and it's not, the freqency table would have
either two or three fields. It might be
frequency_id pk
minutes integer
or
frequency_id
every integer
time_unit text (week, minute, hour, etc)
in fact, the time_unit field might be an id field with a
foreign key relationship to a time_unit table.
To the table that has your user information, add a
frequency_id field.