Synthetic ruby - damaged by heat less than its melting point?
However, would there be any damage to its optical properties?


It is almost guaranteed. Corundum is incredibly sensitive to thermal shock and unless you can do this in a furnace that heats very slowly, it will fracture/crack.

As far as any other properties, your ruby should not see any change in other optical properties for such a short duration, but for longer durations (hours at high temperature) metals can diffuse into the ruby and cause color changes, but I doubt this is an issue for what you describe.