Generally the more serious the offense the more of a barrier is is.
It also depends what type of job it is and the type of check being performed and by who
mostly,the conviction always stays indefinitely in the files of the fbi and states fingerprint systems and the court of conviction, unless a sealing order or expungement has been applied
Generally if you are applying for a job where you will be fingerprinted fir a disqualifying offense(like at my job in NY they check for felonies of sex or violence) and it shows up it's mandated by the state that the employer either fire not not hire the employee. Any lesser offenses not involving a felony of sex or violence will still be reported to the employer, but there is no mandate by the state to take adverse action, and it's up to the employer if they want to take adverse action
If an employer uses a consumer reporting company to pull criminal data on an employee someone from a court, some states have restrictions in reporting certain arrest and conviction information. For example, in NY, a consumer reporting company can report any criminal conviction on an employee for up to 7 years. However, if the employee can be expected to earn $25,000 on the job, the conviction can be reported indefinitely
And if the employer does not use a service and simply obtains the info from the court, the employer does not have to abide by any rules at all
Sometimes there are laws from the EEOC that tell an employer to take into account how long ago the offense occurred, the severity and gravity of the offense, and it's bearing to the job position offered