Quick Jenkins system groovy script to compute how many minutes of build you had in the last N hours

get-jenkins-build-time.groovy

def numberOfHoursBack = 7*24

def totalBuildTime =
  Jenkins.instance.getItems(Job.class).collect { job ->
  job.getBuilds().byTimestamp(System.currentTimeMillis()-numberOfHoursBack*60*60*1000, System.currentTimeMillis())
                              }
.flatten()
.collect { build -> build.getDuration() }
.sum()

def totalBuildTimeInMinutes = (int)totalBuildTime/(60*1000)

println "During the last $numberOfHoursBack hours"
println "\t $totalBuildTimeInMinutes minutes total"
println "\t ${totalBuildTimeInMinutes/numberOfHoursBack} minutes per hour in average"