4 hours.
Just found this in a web search, the most detailed information I seen, the consensus of multiple sites say they just don’t know for sure, but this one says why viruses survive longer than bacteria.
For what its worth:
How long can Ebola live outside the body?
Fwmh
Answered Last
Similar to many things with the Ebolaviruses, their ability to survive outside a living organism is not well-known or studied. Most viruses, contrary to popular belief and the characteristics of bacteria, cannot survive long against the raw elements. The usual influenza or cold virus will survive outside living tissue for about three days, but other viruses, namely HIV, can only make due for a couple of minutes. Ebola is certainly a hardy virus and might be able to make it for over a week but no less than three or four days. So the range is anywhere from three to ten days in all likelihood. The reason viruses die so quickly outside (and bacteria do not) is because, when hit with high-energy electromagnetic waves (for instance, sunlight), they break apart with their abyssal level protection. Since viruses do not actually “eat,” they cannot starve, and they do not get too cold (but can get too hot, for their proteins denature; why did you think we get fevers?). In general, very little is known about Ebola. Even how it is transmitted is unknown.