This is an example how to setup a helper in Home Assistant to convert Meshtastic node uptime from seconds into formatted string.
In Home Assistant settings select Device & Services -> Helpers -> Create Helper.
In Create Helper select Template -> Template a sensor.
Enter a name for the helper and set the State template to:
{{ timedelta(seconds=states('sensor.31ed_uptime')|int) }}
Replace 31ed with the short name of your sensor. The preview shall then indicate an uptime string like 5 days, 18:16:58.