example using civil

package main

import (
        "fmt"
        "time"

        "cloud.google.com/go/civil"
        "github.com/m-lab/go/rtx"
)

func main() {

        ti1, err := time.Parse(time.RFC3339, "2020-05-01T23:59:59Z")
        rtx.Must(err, "failed to parse utc")
        ti2, err := time.Parse(time.RFC3339, "2020-05-01T23:59:59-04:00")
        rtx.Must(err, "failed to parse -4")
        ti3, err := time.Parse(time.RFC3339, "2020-05-02T00:00:01+04:00")
        rtx.Must(err, "failed to parse +4")

        fmt.Println(
                ti1, civil.DateOf(ti1), "\n",
                ti2, civil.DateOf(ti2), "\n",
                ti3, civil.DateOf(ti3))

}