Add Custom Time Frame for Historic Value

In My Collection under Historic Value, the only choices available for time frames are currently All, 3m, 6m, 1y, 3y 5y. Let us enter a custom value, such as the past 15 days, or the past 2.5 years or something along those lines.

i'm asking for this option because I'd really like a "last 30 days" value since I update my collection often and I'd like to see how much it increases each month. Some people update their collection daily even.