allow for more than 0.00s.

Fixes #15149

Change-Id: I1d428a9b3c9bb3d1db8682c53b86e44cecc1dde1
Reviewed-on: https://go-review.googlesource.com/21602Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>