Feasibility of a partially remote postdoc (This question is somewhat related to those answered here and here, but is different in the &quot;partially&quot; remote aspect, and in a few other details I list below.)
I am currently finishing my PhD in theoretical physics in the UK, and have received a funded offer for a 3 year postdoc on the US east coast. I also have at least one postdoc offer from the UK. Both positions come from individual PIs, and are not tied to e.g. teaching requirements.
At the individual group level the difference between the offers is not huge, though I do slightly prefer the US position. However, in my field the US is very strong and active, and I have been advised by my supervisor that it can be a significant advantage to my later career prospects to have exposure to the US scene, especially early on in my career. Ultimately I would be aiming for faculty positions in the UK.
My dilemma is that I have significant ties to the UK (e.g. two-body issues, though no children), and I am not sure whether it is worth disrupting this for the potential long-term benefit of being in the US. One possibility my partner and I have floated is a &quot;partially remote&quot; postdoc. By this I mean something like spending ~2/3 of my working time in the US, and ~1/3 of my working time in the UK. In practice that could mean spending, say, 6 weeks in the US and then 3 weeks in the UK.
I am asking this question because I am wondering whether anyone here has done something like this, and how they found it personally and professionally. Other answers about the balancing of long-term benefits of exposure to the US vs personal situations would also be helpful.
A few notes:

Since my field is theoretical in nature, it is in principle possible to work remotely. Of course there are still significant benefits to working in person, but the hope is that being available in the US ~2/3 of the time would provide enough time to do this, and also get most of the other benefits of &quot;US exposure&quot;.
This question is conditioned on my potential supervisor agreeing to this. They have mentioned that many of their collaborations have been largely remote (even pre-Covid), so they may be used to this mode of working. However, I think this has mainly been with US-based collaborators, so the 5 hour time difference may present an issue.
I have worked out the personal finances of this, and think it would be doable.
I am not sure about the visa and tax implications of this arrangement. My initial impression is that if I am on an H1-B visa then there shouldn't be any visa issues. If anyone has any idea about the tax implications that would be very helpful.
Ask the PI or recruiting HR department
I think the main consideration will be what the PI thinks of the plan. Some PI's want to be able to chat face-to-face to post docs every day, whereas others are happier with a more light touch interaction. This can also vary for the same PI between different projects with different aims. This will be quickly resolved by asking the PI. If you have a job offer there's nothing to lose here.
There may be other issues such as tax, insurance and other employment law things. I'm not an expert but our university has raised issues about staff working in another country even though most staff haven't been to the university buildings at all since March last year. This will be quickly resolved by asking the recruiting HR department. They should be able to give a relatively quick yes/no depending on their own current working pressures.
In long form,

explain as you do here what your constraints and motivations are.
have a concrete plan of how the remote part of the work will go. For example, are you able to shift your working time to be available for meetings during US working hours.
be prepared for the answer to be no.

You seem to have a reasonable fall back plan so I see no harm in simply asking.
Edited to add: You should also be realistic about how travelling will work during the current on-going pandemic. How will quarantine affect your plans? What if you are not able to travel for a prolonged period of time.