How many days does a sale velocity need to remain high to get the organic rank bump?

Hi,

I vaguely remember someone said 8 days but I could be wrong. Recently I have a product that the selling price mysteriously dropped (I believe Amazon did it but I have no proof) 10% causing the sales to triple. Since the profit margin of this product is low and I don’t want to be out-of-stock soon, I prefer to keep this 10% discount for a short period. However I would like to keep it long enough to benefit the ranking. How many days does a sale velocity need to remain high to get the organic rank bump?

Any recommendations/advice is welcome. Thank you.