Run task at specific time

main.go

package main

import (
	"fmt"
	"time"
)

func main() {
	interval := time.Second * 5

	fmt.Println("Starting at:", utc())

	for {
		time.Sleep(calculateDurationUntilNext(interval))

		// Let's assumet his task takes 2 seconds
		fmt.Println(utc())
		time.Sleep(time.Second * 2)
	}
}

func calculateDurationUntilNext(interval time.Duration) time.Duration {
	return utc().Truncate(interval).Add(interval).Sub(utc())
}

func utc() time.Time {
	return time.Now().UTC()
}

// Example output:
// Starting at: 2017-08-12 14:32:43.377570185 +0000 UTC
// 2017-08-12 14:32:45.000228571 +0000 UTC
// 2017-08-12 14:32:50.000234413 +0000 UTC
// 2017-08-12 14:32:55.000214206 +0000 UTC

// If tasks takes longer than interval, for example 6 seconds:
// Starting at: 2017-08-12 14:33:44.819856064 +0000 UTC
// 2017-08-12 14:33:45.000197675 +0000 UTC
// 2017-08-12 14:33:55.000429476 +0000 UTC
// 2017-08-12 14:34:05.000239421 +0000 UTC