It seems there's always a code (or several) out there for 10% off Friends & Family, 16-25 and Senior Railcards (i.e. £30 down to £27), but until 12 October you can get £5 off a F&F Railcard (so down to £25) by using the promo code
"SEFFSEP17".
Note these discounts are only for Railcards bought online via the
Railcard website and sent out by post, and do not apply when buying a Railcard at a station ticket office. Postal fulfilment of orders is normally pretty quick, I'd operate on the basis of a week at most.
(Or are these promo discounts also available for Digital Railcards via the app?)