Since everyone is different, the time you spend studying does not actually help us in making an estimate, if people could make an estimate at all.
What would help is your actual QlikView experience. Did you follow any training (by Qlik) and do you have any hands on experience?
What we usually suggest is follow the QlikView Designer and Developer training and get some hands-on experience.
For more details / advise and for skill assessment, go to this website:
Since you have strong BI experience and you are Tableau certified, this means that you are familiar with most of the BI concepts.
As Onno suggested, the recommended path to follow would be to attend the Designer (2 days) and Developer (3 days) courses and also invest some time working with QlikView in a real project, as most of the certification questions are not straightforward but they are based on real business case scenarios.
I hope this helps
Please also see the QlikView Certification website. On this page you can expand the "exam domain areas" to see exactly which topics are included on the exam and the weight of each topic area to help you prepare. When you pass the QlikView Developer exam you also receive the QlikView Designer certification. We highly recommend hands on experience with the QlikView product before taking the certification exam. QlikView Business Intelligence Certification
You are absolutely correct, Caroline. The Exam Domain Areas are intended to be used as a study guide. There is also an FAQ on the web site with information about preparing for your exam. Hands-on experience is a MUST!
And as Onno and Agis mentioned, investing in training is the best way to begin.
Qlik Certification Program Manager