@bhfn I've only done AS so far but for me personally:
Textbook questions -> Solomon worksheets -> Past papers -> Solomon Papers -> IAL/IYGB
Exam Solutions was also a major help when it came to doing past papers.
I'd also recommend HegartyMaths as his videos are like actual online lessons.
There are also more types of past papers such as IYGB papers, IAL papers and Elmwood papers which you might want to look at.
All links can be found here:
http://www.physicsandmathstutor.com/a-level-maths-papers/As for time, I'd say just make sure you're keeping on top of what you're doing in class for now. Study ahead if need be. Once you've finished all of the content for a module (aka have done all of the textbook questions), you can start answering the Solomon worksheets which will ease you into exam-style questions. And then you can start doing past papers.
I started doing past papers for C1 in January last year, and was doing one a week until about March and then I increased it to two a week and then closer to exams, it was two a day haha. (Still flopped the exam though. I went from 90+ UMS in past papers to 78 UMS in the actual exam. I cry)
This year, I'm hoping to start doing C3 past papers in November and want to complete as many as possible before the exam, so I'll be doing about two or three a week once I start. I'll also be resitting C1 but I won't be preparing for that until January.
Good luck!
Ps. Tip: Buy a planner and plan ahead when you're going to do certain past papers.