Entering final year of undergrad need job advice

I'm just about to finish off my 16 month internship at AMD and enter my final year of studies. I worked at the Markham campus in Ontario on the driver development team and implemented a decent number of features while improving existing ones. I was also involved in working on a lot of the new GPUs we’ve recently launched and making them launch ready. Side note: TC is super poverty so lets not mention it I wanted some advice on when to apply for jobs and how best to prepare for interviews while juggling a full course load in my final year. I'm really interested in applying to Microsoft for their recent graduate software roles as well as Amazon for SDE I (or SDE II if I even qualify). Both companies peak my interests and are working on things I find really cool. So if there's anyone at either of those two companies that got in right after grad I would love your advice on preparing for the interview and when to apply. Anyone else working at other companies feel free to chime in as well since I expect there's probably a decent amount of overlap. Also an Amazon recruiter recently contacted me about internships for the fall term but I told her my current situation and asked about full-time positions to which she responded that full-time postings go up this Aug/Sept. So this kinda has me worried, Aug/Sept seems pretty close for job applications and I feel like I need a lot of prep (i.e. reviewing major concepts, doing lots of LC, mock interviews, etc). Overall I'm inquiring about: 1) When is the best time to apply to either MS/AMZN for recent graduate roles 2) Best way to prepare for them starting now in July and during school. Thanks in advance!