Without a time provided for when their watches were last in sync, their drift can be expressed as:
0.166666666666667 * n
Where n is the total number of minutes between the time when their watches were last in sync and their expected arrival time of 0730.
By dividing their drift of 10 minutes per hour by an hour, then multiplying by the total number of minutes between sync and arrival.
Assume the last time their watches were in sync was 1300 (1pm). This gives us 18.5 hours until they need to arrive at work again (0730 the next day). So, we translate this to 1,110 minutes and then multiply by 0.166666666666667 to get the total drift of 185.00000000000037 minutes. So, by time 0730 rolls around, the employee with the fast watch will have been at work for approximately 3 hours and 5 minutes. Meanwhile, the employee with the backwards watch will not be at work for another approximately, 3 hours and 5 minutes.
Lateral Thinking Answer
Assuming that their watches are in sync and that they’re both aware of the issues with their respective watches:
They won’t be off at all. Simply because the same amount of time has passed for both employees, so drift doesn’t matter. One goes backwards the same amount that the other goes forwards by. Assuming that the employee whose watch goes backwards is aware of their misdirection, then they would still arrive on time.