More likely he wanted an extra day off during the week, to spend in Houston.
This probably wouldn't be that big of a deal if Chan wasn't in his first year, trying to establish himself and a new defense. In other words, had Chan been here for a couple of years, this might not even come to light, as they would likely accommodate Schobel. (I am speculating, of course.)
I can understand Schobel's position, as well as the Bills'. It just may be the right time for him to retire. If it takes him another few weeks to decide, I'm OK with that, too.