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Cron expression for every 100 minutes

Could some one help me to create a cron expression to run schedule a hangfire job for every 100 minutes like 1:40, 3:20, 5:00 so on…

Cron is not meant to solve such problems. It defines the exact date and times, when a trigger must be fired, not intervals.

Another solution to your challenge might be to schedule MyClass.MyJob() to run with cron: 0 0 30 2 0 (never). This allows you to start your job manually whenever it doesn’t run or isn’t scheduled anymore.
At the end of yor job, you schedule it again to run in 100 minutes.

class MyClass 
{
    public void MyJob()
    {
         ... do you job here ...
         
        BackgroundJob.Schedule( () => MyClass.MyJob(), TimeSpan.FromMinutes(100) );
    }
}