This is how it looks on my machine:
ufechner@framework:~/.juliaup$ cat juliaupself.json
{
"StartupSelfUpdateInterval": 1440,
"ModifyPath": true,
"JuliaupChannel": "release",
"LastSelfUpdate": "2025-01-16T15:01:53.563126929Z"
}
Note that the time string is somewhat different and has a Z at the end.