We should discuss if we want to remove this feature. In Facter 4 it works as it did in Facter 2. It seams that it was removed from Facter 3 because it was hard to guarantee it with native code https://tickets.puppetlabs.com/browse/CFACT-44
Facter 3 doesn't support timeout option for custom facts, it logs a warning message when a user tries to set that option. We decided to keep the mechanism that sets timeout on resolution on Facter 4 and to add an acceptance test to verify that the behaviour is indeed as expected.