package main

import (
    "fmt"
    "math"
    "time"
)

func calcDuration(hrStart, minStart, hrEnd, minEnd int) (hrDiff, minDiff int) {

    // next line crashes on Win7/go1.3, systemcalls not supported:
    //pt, _ := time.LoadLocation("Europe/Lisbon")

    //this works fine:
    pt := time.UTC

    yr, mo, dy := time.Now().Date()

    t1 := time.Date(yr, mo, dy, hrStart, minStart, 0, 0, pt)
    t2 := time.Date(yr, mo, dy, hrEnd, minEnd, 0, 0, pt)

    overallDiff := t2.Sub(t1).Minutes()
    hrDiff = int(math.Floor(overallDiff / 60))
    minDiff = int(math.Mod(overallDiff, 60))

    return
}

func main() {

    hr, mi := calcDuration(8, 15, 19, 35)
    fmt.Printf("Duration: %d hours and %d minutes.\n", hr, mi)
}