@jrcoutinho - One of the option is to actually assign task to both approvers main and secondary. If main approve does not response, secondary can act.
For delegation design you are on below, you can run a do until loop and change timeout settings. Then you can add a pause of 15 mins or so that action does not time out. Then in the loop towards end, check created date of approval and compare with todays date. If its > 3 days, set some variable so that when loop runs again, you can reassign the task to another approver. I know it sounds complex, but try this route.
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after sleep over on it, i decided to set a variable with SKIPPED value on the secondary approver.
As i have a flow for for the delegation, where after 3 days the main approver time out (set up on the setting of the action) and the secondary approver runs after the time out, if the secondary runs i have the info SKIPPED set on the variable and then i can use it to perform another action later in the flow