log: fix sequencer latency metric (#688)
log: fix sequencer latency metric (#688)

Just capture start time so deferred code calculates correct
overall time, rather than calculating the time when defer
is called.
AlCutter/trillian,gdbelvin/trillian,Martin2112/trillian,gdbelvin/trillian,Martin2112/trillian,RJPercival/trillian,codingllama/trillian,daviddrysdale/trillian,AlCutter/trillian,codingllama/trillian,Martin2112/trillian,google/trillian,google/trillian,daviddrysdale/trillian,RJPercival/trillian,daviddrysdale/trillian,gdbelvin/trillian