Can i use a hair relaxer to make my hair wavy and not straight?

Especially for hair products containing strong chemicals meant to change the structure of the hair, only use the product for its intended purpose, specifically following the instructions to the letter. Do not use a product for an unintended purpose and making up one's own instructions.

If the desire is to achieve wavy hair then use a product that has that as its goal and follow the instructions. It is likely to be less harsh than a product meant to straighten hair.

Altering the time the product you have already purchased is in the hair might or might not work in the manner suggested in the question; there could also be a multiple set of timed reactions that take place and leaving the product in less than the suggested time might bypass a final stage that repairs the altered hair and instead of wavy hair, could end up with more damaged straight hair whereas leaving it in the recommended time would result in less damaged straight hair.

Strongly suggest going to an experienced professional since it appears your hair has not been previously relaxed.

There is no evidence that anything a person does can alter the rate of growth set by inherited DNA. Hair only grows at an average rate of 1/2" per month.

Good Luck!

I have very thick, tight curly hair. I did not want to straighten it. My stylist used a perm and rolled my hair snug on larger rollers (not the rods normally used for perms). It tamed my hair a lot and loosened the tight natural curls. Maybe you could try it on larger rollers instead of combing it straight.