How to run a schedule job when a user log in the instance? What should be the condition

[dpac_nick]

If requirement is to execute some script when user logs in, there is an oob event "login" which is fired when user logs in it can be associated with script action to execute the script.

https://docs.servicenow.com/bundle/washingtondc-platform-administration/page/administer/platform-eve... 

[Mark Manders]

Why do you want to run a scheduled job when a user logs in to the instance? That could cause huge performance issues. 

The last login on the user record changes when a user logs in, so maybe you can use that, but I would really look at your requirement and the reason you are going for this solution and just shoot it down if there is no other way to resolve it.

[Rosy14]

I want to set a field value based on user. There are table where for all records i want to set. How to achived it?

[Mark Manders]

I gave you a possible trigger, but again: don't do this. It will cause you performance issues.