Trending @Infosys; When is the best time to resign or switch without offer letter

I am having 2.4 years experience. I have been trained in cyber security and reskilled in security testing. Currently doing manual testing and sick of it. Currently upgrading my skills in security testing. The salary they are paying is not sufficient to survive in tier 1 cities. I don't want to work for more hours with less pay. When is the best time to resign or switch from Infosys. When will the hiring starts.