"Build duration" in host properties shows "N/A"

“Build duration” in host properties shows “N/A”

Expected outcome:
Host properties should show some number of minutes / hours it took to build.

Foreman and Proxy versions:
Foreman Master 1.20.1, Foreman TFTP proxies: 1.20.1

Foreman and Proxy plugin versions:

Other relevant data:
[e.g. logs from Foreman and/or the Proxy, modified templates, commands issued, etc]
(for logs, surround with three back-ticks to get proper formatting, e.g.)