Dear Vignesh,
The criteria for issuing service certificate vary organisation to organisation. It all depends on the probation, service rendered, the time of the employee adjusting to the organisation, his/her values and organisational commitments. Yet, a service certificate cannot be issued for one day or before completing probation period as no Manager can access the reliability and work efficiency, however, they issue service rendered in an organisation with the motive best wishes for the future endeavours..
Best Wishes....