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Ine way nesting - different starting date

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I am trying to implement a one way nesting simulation with WRF. The purpose of the simulation is to run a larger grid simulation for the full day, identify the periods affected by rain and run a nested domain only for these periods of time.

My input data are ERA5 (ECMWF) with a time frequency of one hour.
Thus I have only the input values for 00:00 01:00 02:00 03:00 04:00 05:00 06:00 ...
I save the result of my coarse domain every 3 minutes (wrfout files).
Then I would like to start my nested domain run at 3:33 for example.
My problem is that I cannot create an adequate metfile starting at 3:33 in order to initialize the run because my input data (and thus the "FILE" files) are still corresponding to the input data of the coarse domain and thus available every hour.

Is it possible to implement such a method with WRF, or should I always start my nested runs on the hours ?

Thank you very much for your help
One option is that, you may run ungrib and set the time interval to 3 minutes. ungrib has the capability to interpolate data to the time you specify. This will give you input data for ndown run. Please try and let me know whether it works for you.