Vacuum cementing apparently is far more likely in space than on a planetary surface in atmosphere. How long must two surfaces be kept in contact with each other in a vacuum for vacuum weld/cementing to 'take'?
Instantaneously given the initial conditions are right, such as the materials:
Temperature would affect the rate of bonding. Perhaps insignificantly.
Consider also the case of the machining lathe, where a cold weld can occur between the metal and tool, because the metal had not interacted with the air yet to become passive, there is no lubricant, and the tool being spun too slow .