are the dates fixed? like every 3 weeks, always on a monday etc? if so then you will need to make some kind of confirmation of what email needs to be sent each time the flow is triggered. the recurrance timer should trigger at the smallest intervals between dates. realistically it would be easier to make a sharepoint list that contains a column with the recipients emails, the content of the email and a description of the dates it needs to be sent, could be a day , number of month etc. then the flow triggers daily and only retrieves records where the current date matches the send date data, then setup the email with the rest of that records data. An easier way would be a flow for each separate email timer. So all emails sent weekly get a flow, all daily emails get a flow, all quarterly emails get a flow etc.
