The OR will advise you on when the IPA/IPO payments are due to start. Have you declared a disposable income of more than £100 a month on your Statement of Affairs?
Given the level of disposable income, it is more than likely your are looking at between 50-70% to go to the OR every month for the next three years. The OR will let you know when it is to start, but it is usually straight away following the OR meeting.