Thanks, I realized I had not looked carefully enough at the receive node docs. The messages I needed have no # hashtag. I was able to adapt your flow to give me the latest update to the user's (@bowenferry) bot timeline by checking every 5 minutes during the scheduled ferry runs.
[{"id":"27a10abd9f6cf7ce","type":"inject","z":"3754c020.afda5","name":"Every 5 minutes","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"*/5 4-22 * * *","once":true,"onceDelay":0.1,"topic":"","payloadType":"date","x":110,"y":220,"wires":[["a62853eec8740870"]]},{"id":"a62853eec8740870","type":"http request","z":"3754c020.afda5","name":"Mastodon @Bowenferry","method":"GET","ret":"txt","paytoqs":"ignore","url":"https://mstdn.ca/@bowenferry.rss","tls":"","persist":false,"proxy":"","authType":"","senderr":false,"x":510,"y":220,"wires":[["70f6c3f59b601ee3"]]},{"id":"70f6c3f59b601ee3","type":"xml","z":"3754c020.afda5","name":"","property":"payload","attr":"","chr":"","x":90,"y":280,"wires":[["fb8f71fc05e984fc"]]},{"id":"fb8f71fc05e984fc","type":"change","z":"3754c020.afda5","name":"Extract latest update","rules":[{"t":"set","p":"payload","pt":"msg","to":"payload.rss.channel[0].item[0].description[0]","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":280,"y":280,"wires":[["a1da5687476eb4b4"]]},{"id":"a1da5687476eb4b4","type":"function","z":"3754c020.afda5","name":"Remove HTML tags","func":"msg.payload = msg.payload.slice(3, -4);\n\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":520,"y":280,"wires":[["cadac481.c68368"]]}]