As per the Applicant Guide, applicants are given 48hours to accept or reject their offers on Oriel.  


You will be given the option to Accept , Accept with Upgrades or Decline .  If by the deadline of the 48hours you have not decided on your offer, the system will assume that you do not want the job and will decline on your behalf.   Once this happens, you will be removed form the recruitment process and the job will be reoffered to another applicant