Add proper support for time intervals in recurring jobs

[odinserj]

Since Cron.XXXInterval methods should be deprecated as per #1041, a question arises – how to handle intervals then? One could use ScheduledState to create a job and re-schedule after each completion. But this is not an obvious option, and could lead to much more non-obvious consequences like 5 retries or an original job caused 5 scheduled jobs to be created instead of 1 with a simple implementation.

Instead, recurring jobs should be modified to support the following recurring schemes (yes, there will be no support for seconds yet). This is just to handle simple cases, with a simple implementation. Since recurring job is a has, we could save backward compatibility without any problems.

1. Every X minutes
2. Every X hours at MM minutes
3. Every X days at HH:MM
4. Every X months at DD day at HH:MM

[crawdell]

I'd like to propose something I've done before to handle cron intervals. I needed a solution to "every 2 weeks" when using Ncrontab Advanced and so I extended the functionality to allow for "Xnn" to be added to a cron expression.

Example:
00 00 * * FRI X2

Without "X2" this would just be every Friday at midnight. But with X2 I would getnextoccurance 2 times and use the second value as the next run time which would be 2 weeks.
This can be useful for doing all kinds of new variations. It can also lead to confusing results sometimes if you don't think about your expression carefully but that's true of all cron expressions.

This I think helps fill in a gap that cron has and has been very useful for my scheduled jobs. Now that I'm using Hangfire I'll love to see this included. The good thing is you can use this with any cron expression and just use a multiple X3 to get it to do what you want.

30 * * * * X3 would be every 3 hours at 30 minutes past the hour.

I'm on the 1.7.0 beta and it works great. If this could somehow be added that would be very helpful. If not I might try my own version with the source either by extending Hangfire or more likely Cronos.

[I posted this in another response as well. Sorry if this confuses, I didn't see this issue then]

[antgel]

Does anybody plan to work on this extremely useful feature? Something like "every x weeks from date y" would be great.