Fix build script

[shu-mutou]

In MacOS, date command does not have %N option.
We do not need elapsed time in nanosecond.

Related: #4128

[codecov]

Codecov Report

Merging #4258 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4258   +/-   ##
=======================================
  Coverage   46.56%   46.56%           
=======================================
  Files         200      200           
  Lines        9366     9366           
  Branches      105      105           
=======================================
  Hits         4361     4361           
  Misses       4736     4736           
  Partials      269      269

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[maciaszczykm]

/lgtm
/approve

Thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: maciaszczykm, shu-mutou

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