Parallel action will always wait until each parallel string is completed. I don't think it will work this way. If you are just after the reminder mails I'd suggest you try flexi task.

By default it will create approve/reject branches but you can stop it doing so by going into its settings, hit Advanced Options and turn on Do not create branches

Now you have a plain action without any branches and you can use the default Reminders in the ribbon to remind assignees if the task has not been completed yet.

If you use a default SharePoint Form you're set. If you use a Nintex Form instead you will need to remove the outcome control as you do not have any approval here and edit the Save-Buttons settings like this to make it behave like the button in the request review action:

you can place reminder action into a loop that will regularly in reasonable periods check whether there is already time to remind elapsed. if so, it will send reminder, if not it will pause for a delay period.

Thanks a lot