If you set up and hourly or minutely schedules the server start time works a little different than for all other schedule types. In this case, the start time is only used determine the first time a schedule is executed. The schedule will hereafter at the minutely/hourly interval without looking at the start time.
in case of a schedule´s start time and start date is elapsed, the schedule will run instantly and hereafter run at the specified interval from this time.
This means that if you have different schedules of these types there can conflict with each other you need to give them both different start times and different recurrence intervals to lower the chance of the schedules conflicting.