This depends on a couple of things. First, it depends on what type of background check your employer will be doing and whether they will be getting a copy of what's called your TCIC/NCIC report. The TCIC/NCIC report is your official criminal record kept by State and Federal agencies. If they use a service that accesses your TCIC/NCIC report, then the second thing would be whether or not your were arrested on the offense. If you were arrested, there will be an entry on your TCIC/NCIC record that shows that your were arrested for whatever particular felony you have been (or may be) charged with. Therefore, it's possible that your potential employer will see, at least, that you were arrested for the offense (even though you haven't been convicted). There is no set "time" for that to show up on your record, but generally, once it is entered into the system, it will automatically be on your record at that point.
A charge is on your record immediately - regardless of whether or not you have been convicted. You need a lawyer representing you on your criminal case that you can talk with.