Cooking ham in an oven with oven cleaner

Since it's already fully-cooked, you don't need to be all that precise with time or temperature. The most important thing is to avoid drying it out, so use a roasting pan and add a little water to the bottom (not more than 1 cm) and cover it while it's reheating.

It's best if you have a meat thermometer; toss it in at 300° F / 150° C (or up to 350° F / 175° C if you're in a hurry) and aim for a temperature of about 140° F / 60° C. If you don't have a thermometer, this about.com page suggests 16-20 minutes per pound; it also suggests heating to 135° F which is also fine. But if you're not going by a thermometer then you'd better make sure that it's completely thawed first, all the way to the interior, lest you end up with a semi-frozen dinner.

If you also plan to glaze it then apply the glaze after it's been heated and raise the temperature to 400° F (205° C) as the above link suggests.

This is really an issue of risk.

The USDA's recommendation is not to consume meat that has experienced more than four hours of cumulative time between 40° and 140° F. Essentially, that means that the level of risk of illness from food-borne pathogens is acceptable in that range. The government's position is that 5 hours beyond a level of risk that they are willing to expose the public to.

Also be aware that (sliced) deli meat is more prone to pathogens that a whole ham.

That said, it comes down to what level of risk you are comfortable with. Personally, I would probably eat it myself, but not serve it to others.