How long do you wait between trying new products? (more details in description below)

I just won the SKIN1004 brightening toner and ampoule, but I have to post a review for both of them by January 6th. I’m thinking of using the toner for two weeks and then switch to the ampoule for another two weeks so that I can have ample time to write a review for both products. This way I’ll be able to see how effective each product is without having to guess which one works for my skin if I were to use them at the same time. If anyone else has a better idea then please let me know! ☺️💞