Automation time pattern triggers should use Cron expression. At least standard Cron expression (cron - Wikipedia) and maybe some non-standard characters (cron - Wikipedia).
This feature will provide more flexibility in triggers. The documentation could refer to the Cron documentation. A simple search with your favourite search engine could help you to find the right syntax. It could also simplify implementation in the core, just by using Cron directly.
This feature will massively reduce complexity in my automation time pattern triggers.