When installing macOS Sierra it is showing -22 seconds and it has been for some time. What should I do now?

I've had a few instances of "Less than a minute remaining..." take an hour to complete.

So, when you get really tired of waiting, wait a bit more thenI guess you'll have to restart & see what happens.

It is Apple's test of your patience. Give it as much time as it needs to successfully complete.

So you know, phase one is the OS download which may typically take up to an hour, more or less. Phase two is the installation which typically can take up to 45 minutes, more or less, with several automatic restarts.