There is no filter to influence the output of the ACF time field. You can set the return value in the ACF field settings. In my case, the set format is returned, even if I change it afterward.
Time output isn’t just needed on the front end, it’s needed for accessibility and semantic HTML.
The HTML <time> element needs datetime= attribute. The value of this attribute must be in a machine-readable format. Of course, we never want to use machine-readable format on the front-end. So, we absolutely need control over the output.
I absolutely agree with @digitalgravy. This is especially confusing for users, since all native date fields support the formatting out of the box. I think from the end user perspective, it is expected to have this consistent with all date fields.
Also, i do have the case where I want to display different formats of the same date field throughout my site.