Anyway to run an action on entire inbox automatically for a specific time? Or run a action on entire inbox at once…
You could probably schedule a Shortcuts shortcut to run a Drafts action unattended (scheduler of your choice and a Shortcuts command line call) on a schedule. I think on an iPhone or iPad, you would be prompted to run it. The shortcut could use Drafts steps to retrieve the set of drafts you want to process, and then iterate across the set and run a specific action against each draft.
Read this section of the docs for details on Shortcuts and Drafts.
Read this for Shortcuts on the command line.
If you select and hold on select, you can select all drafts and select to run an action as an operation on each draft.
See this section in the docs.
Hope that helps.