I would like to suggest few things, however these are my views and some people may differ from me, First of all sketch out a plan for next 30 days as to how much topic you need to cover each day, set a target for each day. Dont forget to cover the RTPs of current exam and atleast last two RTP's
1. Costing- As your first paper will be costing, you can leave short topics like service sector costing, Life cycle Costing, target costing etc to be completed in last 5 days so that you will not have to revise it again. In costing go for concept clarity rather than solving numerous questions. Give some time for theory questions too. Complete OR/ QT part first and dont give much time to relevant costing part, as the questions from relevant costing takes a lot of time in exams and a single mistake can ruin your whole solution.And Regarding 15 min of reading time in exams, devote just 5 min for going through the whole paper and then start reading a lengthy problem so that you can start answering as soon as you receive the answersheet, it will save time
2. ISCA- Sorry , for ISCA I cant say anything
3. DT - DT is very very vast so no matter how much time you give to DT , it will be still less. So fix a slot of 3-4 hrs each day for dt and study dt in this slot every day without fail. After every four days use one day for revising what you have studied earlier. And go with confidence in DT no matter how much you remember the topics before exams
4. IDT - Revise in following Sequence
1. Service Tax and VAT
2. Case Laws and numerical questions from Excise, Custom .ST and Vat
3 Custom and then touch the excise portion
Hoping the above may help you clear the exam , Good Luck