Discount Code for Digital-Product For 3 Months

Hi All,

Is there a way to set up a discount code, which can be used against a digital product for a set period of time. For example, I run a monthly subscription on my website. I want to offer people the opportunity to sign up for 3 months at a reduced cost. I would think a discount code the best way to do this but I can only set up a code for the first month or for all instances and nothing in between. Is there a workaround whereby I can offer my students a chance to sign up for the first 3 months at a reduced rate and then it automatically goes back to the full price? If not, what are my options?

Thanks