ah.. date and time domain.. :) i'm tired and wish some day everyone will live in UTC

Of course with that approach you will almost certainly get jobs that are run twice a night once a year and not at all once a year.

Why? When a scheduled job is run, the value in the column NextExec in the database table tblScheduledItem get its value updated. 

If adjustment for daylight saving time is taken into account when NextExec is updated, this should be possible without the kind of problems you describe.

For jobs where a fixed interval (f.ex every 24hours) is required, it should still be possible to run the jobs by UTC time.

I can't see how something like this will make some jobs run twice, or not at all, once a year...

    public void RunMyScheduledJob()
    {
        var nextExecFromDatabaseLocal = GetNextExecTime();
        // RunJobIfTimeIsInThePast(nextExecFromDatabaseLocal);
        var newNextExecTimeUTC = CalculateNextExecTime(nextExecFromDatabaseLocal, new TimeSpan(1, 0, 0, 0)); // 1 day
        // UpdateDatabaseWithNewTimeUtc(newNextExecTimeUTC);
    }

    // Display this value in the UI, local time
    private DateTime GetNextExecTime()
    {
        var nextExecFromDatabaseUTC = new DateTime(2018, 3, 24, 11, 0, 0, DateTimeKind.Utc); // 24. march 2018, 11:00 UTV
        var nextExecFromDatabaseLocal = nextExecFromDatabaseUTC.ToLocalTime();
        return nextExecFromDatabaseLocal;
    }

    private DateTime CalculateNextExecTime(DateTime lastExecutedLocal, TimeSpan interval)
    {
        var nextExecutedLocal = lastExecutedLocal + interval;
        var nextExecutedUTC = nextExecutedLocal.ToUniversalTime();
        return nextExecutedUTC;
    }

Correct, if adjustments are done for next execution. That wasn't clear in your OP.

Now I am even more confused about what you actually request, you no longer wishes all jobs to be run in local time or having a site-setting dictating local/UTC but rather controlling it differently for each job?

I just want to schedule my jobs by local time.

That can be implemented in a number of ways. Some examples:

• Always run jobs by local time
• Let a global setting select local time or UTC
• Let a setting for earch scheduled job select local time or UTC