JoDee, This is my own opinion as a patient. It is what works for me.

I am on an 8am 8pm schedule because that is best for me to live with. That is what I have set on my phone alarm. I do regularly need to make adjustments because of daily activities. And I am comfortable with adjusting 30 - 60 min when I do this. For example, every Sunday, I take my morning dose at 7 instead of 8.
Whenever I'm surveyed about taking my meds, I always get asked if I have 1) missed any doses 2) been more that 1-2 hours late/early with my dosage.
The aim is to have a stable dose of the anti-rejection meds in our body at all times I was told by someone (?) somewhere along the post transplant a slight deviation here and there would not be problematic.
I choose to keep as close to 12 hour interval as possible. And If I know in advance, I feel more comfortable making 30 minute shifts.

I hope this is somewhat helpful.