If you just wanted the messages sent at fixed times, you could use a time-based rule to send them. Someone else asking how to do that had a sample rule that would run at the right time, and then use the commands in the rule that Opus sent before.
I’m not sure what you’re looking for with the time picker, or where you’d expect to find that. There isn’t a date time or time picker in the sitemaps or in HABpanel. You’d have to get really creative with a bunch of simple integers and then building the string you need from them in a rule. Getting it into the UI is harder than it sounds.
OpenHAB seems to be really good at making things happen when conditions are met, but not as effective at user interactions.