On the ILL request form in OPAC we have a "Last date required" field. To specify the default date for this field:

1. From the Module Menu select Maintenance, Requests and then General Parameters.
2. Set the ILL last date required default days.
3. Click Save & Close.

For example, if today's date is 5/3/18 and ILL last date required default days is 30 then an ILL request placed today via OPAC will have 4/4/18 by default in Last date required.