Bhyve as of r279225 (FreeBSD -CURRENT) or r284894 (FreeBSD 10-STABLE)
supports using UTC time offset via the '-u' argument to bhyve(8). By
default it's still using localtime.

Make the bhyve driver use UTC clock if it's requested by specifying
<clock offset='utc'> in domain XML and if the bhyve(8) binary supports
the '-u' flag.