An eating window of 6 hours is still pretty constrained, compared to what most people do (eat during all the hours in the day).
That said - this is going to differ widely per person.
For most people though: Starting from scratch (aka eating from breakfast till bedtime), I would definitely recommend a 6 hour window over going straight OMAD. Just because it’s a less dramatic change. The body needs time to adapt. Also - you should only do OMAD if you already know you can handle a 6 hour eating window.