A problem with BI publisher reporting jobs sequence

I have a problem with BI publisher reporting jobs sequence. I want to
synchronize reports so that there is no big load at the server in a time, but I
want to run the reports with interval of minutes. So I assumed that I can set the
staring time of a sets of report one minutes apart, e.g. every 15 minutes. However,
the job scheduler does not work as expected, but the minutes are started to
count from every full hour. Also even odder, all the reports are running at
full hour. E.g. if I set the time interval as 50 minutes, the report will run