The problem is many subjects, not one
GCSEs differ from most exams in that you sit a lot of them across a few weeks, which makes the scheduling problem harder than the studying problem. Working one subject to completion before starting the next leaves the early ones cold by the time you sit them. Rotating subjects across the weeks handles that directly, and it happens to match what the spacing research supports: returning to material after a gap retains more than a single unbroken block, even though the block feels more productive at the time. Build the rotation once, early, and follow it, because rebuilding the plan every evening is how the plan stops existing.
Work from your own board's specification
England has several awarding organisations — AQA, Pearson Edexcel, OCR, WJEC Eduqas — and the specification differs between them for the same named subject. Your teacher can tell you which board each of your subjects sits, and the board publishes the specification and past papers for it. That specification is the source of record for what is examinable, and a revision guide bought for a different board is a real and common waste of weeks. Ofqual regulates the qualifications and publishes how grading works. Past papers from your own board are the most useful single resource, both because they are accurate and because working them is retrieval practice rather than rereading.
Plan for the exam weeks themselves
Once your timetable is published, work backward from it: a subject with a paper in the first week needs its heaviest revision earlier than one sat in the last. Two papers in one day is common, and it is worth knowing which days those are before you meet them. Keep the final days before each paper for review of things you already know rather than for new topics. Sleep and food matter more across a three-week exam period than across a single test, because the fatigue accumulates. The exam-day checklist in the free kit covers equipment and the practical items so nothing needs deciding on the morning.