As mentioned, the clock starts ticking from the end of the month in which you take your first exam (but you can take as long as you want to prepare for it).
The accepted rate of study is fifteen hours per week, so for the ATPL(H), it will be 11 months, or if you can manage Mon-Fri, 9-5, somewhere between 5-6 months. As the fixed wing has more material, you can stretch that a bit.
Phil