You can negotiate and offer "anytime" before you accept and start. As long as you have not accepted the offer letter, the whole 'negotiation' is still in play.The first step of the process is to write a reply letter (or email, if that's how your offer was sent) to ask for your desired salary. You interviewed and it turns out the company wants to hire you. Never accept the first offer, right away. In the end, always be sure to keep it brief, reiterate your salary, benefits, and start date, thank the hiring manager, and proofread everything! Salary negotiations are collaborations, not conflicts. You can be gracious, polite and grateful while also being confident and persuasive. It can also make it easier for you to draft up an official acceptance letter in response. Salary negotiations are time sensitive.