Single entry variable on order date--right click on it--Restrict---Show--Value Ranges--Between--Choose the single entry variable in from and to --Give offset of -30 to 0.
I tried this only before, but it was giving error regarding interval and this seem to work only with the created variable as an interval. In my case, user needed Single date entry and hence between operator in value range was not working.
Used the < and > operators for this date and used offsets is what I meant, but then since we don't get interval reference, had to make 2 calculations and then another cal for the interval