And because you caught me bored at the end of the week and because it was an interesting excercise, here is a more complete example:
[{"id":"9be1f49f.37f098","type":"subflow","name":"UI Time Input To Cron","info":"","category":"","in":[{"x":60,"y":80,"wires":[{"id":"fb4ea2b7.8f275"}]}],"out":[{"x":320,"y":80,"wires":[{"id":"fb4ea2b7.8f275","port":0}]}],"env":[],"color":"#DDAA99"},{"id":"fb4ea2b7.8f275","type":"function","z":"9be1f49f.37f098","name":"","func":"const out = {}\n\nout.input = msg.payload\n\nconst dt = new Date(msg.payload)\n\nout.hour = dt.getUTCHours()\nout.minute = dt.getUTCMinutes()\n\nout.cron = `0 ${out.minute} 0,${out.hour} ? * * *`\n\nmsg.payload = out\n\nreturn msg;","outputs":1,"noerr":0,"x":190,"y":80,"wires":[[]]},{"id":"6b009717.947618","type":"debug","z":"63281c77.40a064","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","x":710,"y":1420,"wires":[]},{"id":"1b4b05f0.7fdf3a","type":"ui_text_input","z":"63281c77.40a064","name":"","label":"Start","tooltip":"","group":"fa3eee85.b8eb1","order":3,"width":0,"height":0,"passthru":false,"mode":"time","delay":300,"topic":"start","x":310,"y":1420,"wires":[["42c8160e.52b738"]]},{"id":"818949b1.1eff98","type":"ui_text_input","z":"63281c77.40a064","name":"","label":"End","tooltip":"","group":"fa3eee85.b8eb1","order":3,"width":0,"height":0,"passthru":false,"mode":"time","delay":300,"topic":"end","x":310,"y":1460,"wires":[["cfa735d3.457d78"]]},{"id":"eaba0840.cc84f8","type":"debug","z":"63281c77.40a064","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","x":710,"y":1460,"wires":[]},{"id":"177ea815.3a30f8","type":"inject","z":"63281c77.40a064","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":120,"y":1420,"wires":[["1b4b05f0.7fdf3a","818949b1.1eff98"]]},{"id":"42c8160e.52b738","type":"subflow:9be1f49f.37f098","z":"63281c77.40a064","x":500,"y":1420,"wires":[["6b009717.947618"]]},{"id":"cfa735d3.457d78","type":"subflow:9be1f49f.37f098","z":"63281c77.40a064","x":500,"y":1460,"wires":[["eaba0840.cc84f8"]]},{"id":"fa3eee85.b8eb1","type":"ui_group","z":"","name":"Time","tab":"70bd0808.2b4f68","disp":true,"width":"6","collapse":false},{"id":"70bd0808.2b4f68","type":"ui_tab","z":"","name":"Schedule-Test","icon":"dashboard","disabled":false,"hidden":false}]
Just needs cron-plus adding in now.
