No impact. Time is used throughout httpd to measure progress in terms of deltas between the beginning and end of a request, and similar.
Requests in-flight during the LeapSecond may exhibit negative processing time durations, in some cases these may be represented by third party modules in an unsigned form. This may confuse log parsing with some user-specified complex log format statements, but causes no errors in data collection.
There are no operational errors expected. The httpd server regularly observes small time adjustments during the normal course of operation, where the system clock is re-synchronized to the reference clock. This has been an anticipated behavior since the software was initially created in the mid '90s.