Difficult to estimate these as each legislation is different.
I also presume, Bahrain is not a seeded legislation.
So you will have to write all the tax rules and reports.
But, as the Tax/NI rules for GCC are fairly simple, should not be difficult.
Best way to go about it, is to do it in phases.
Core HR - BG configuration, Person migration, Absences etc.. and finally any reports for HR
Payroll - elements, balances, formulas and all the logic.. and then all the reports.
Once HR and payroll are done.. SSHR and OLM should take 1/3(or 1/2) of the time you spent on the HR/Payroll.