This still happened to me with Jenkins ver. 2.73.3, Windows Server 2012r2.
Created a cron expression: 0 22 * * 1-5
or: H 22 * * 1-5 (as jenkins suggests to use "H"), the scheduled backup never happened. It worked only when triggered manually.
After posting this comment, I updated Jenkins to ver. 2.89.2 (there were some security updates pending, and it was recommended to update Jenkins (LTS) from 2.73.2 to 2.89.2) and now the scheduled backup works according to the cron expression.