fix recently added time sensitive tests failing with valgrind (#7512)

interestingly the latency monitor test fails because valgrind is slow
enough so that the time inside PEXPIREAT command from the moment of
the first mstime() call to get the basetime until checkAlreadyExpired
calls mstime() again is more than 1ms, and that test was too sensitive.

using this opportunity to speed up the test (unrelated to the failure)
the fix is just the longer time passed to PEXPIRE.