I am not a hass.io user but I tested your setup on my test hass.io server and it seemed to created the snapshot with the correct name just fine.
[{"id":"3aedc0f6.6417a","type":"api-call-service","z":"5eb3594f.d294b8","name":"","server":"ef067c6f.620e6","service_domain":"hassio","service":"snapshot_full","data":"","mergecontext":"","output_location":"payload","output_location_type":"msg","x":462,"y":656,"wires":[["b74fe511.585188"]]},{"id":"3da426b1.6c6bda","type":"inject","z":"5eb3594f.d294b8","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":108,"y":656,"wires":[["2229a92f.126cd6"]]},{"id":"b74fe511.585188","type":"debug","z":"5eb3594f.d294b8","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","x":678,"y":656,"wires":[]},{"id":"2229a92f.126cd6","type":"function","z":"5eb3594f.d294b8","name":"","func":"msg.payload = {\n \"data\": {\n \"name\": (new Date().toISOString().replace(':', '_').replace(':', '_').replace(/\\..+/, ''))+\"_Snapshot\"\n }\n}\nreturn msg;","outputs":1,"noerr":0,"x":258,"y":656,"wires":[["3aedc0f6.6417a"]]}]