Timestamp Flag

Using the timestamp flag is simple. Please refer to time.Parse to get possible formats.

package main

import (
    "fmt"
    "log"
    "os"

    "github.com/urfave/cli/v2"
)

func main() {
    app := &cli.App{
        Flags: []cli.Flag{
            &cli.TimestampFlag{Name: "meeting", Layout: "2006-01-02T15:04:05"},
        },
        Action: func(cCtx *cli.Context) error {
            fmt.Printf("%s", cCtx.Timestamp("meeting").String())
            return nil
        },
    }

    if err := app.Run(os.Args); err != nil {
        log.Fatal(err)
    }
}

In this example the flag could be used like this:

$ myapp --meeting 2019-08-12T15:04:05

When the layout doesn't contain timezones, timestamp will render with UTC. To change behavior, a default timezone can be provided with flag definition:

app := &cli.App{
    Flags: []cli.Flag{
        &cli.TimestampFlag{Name: "meeting", Layout: "2006-01-02T15:04:05", Timezone: time.Local},
    },
}

(time.Local contains the system's local time zone.)

Side note: quotes may be necessary around the date depending on your layout (if you have spaces for instance)