Qatari projects typically use FIDIC-based conditions, often with Particular Conditions that adjust the certification and payment periods. Payment runs through the Engineer's Interim Payment Certificate, counted in calendar days. Always read the Particular Conditions, because they routinely change the FIDIC default periods.
Not your whole portfolio. One live job, one certificate. If it does not save you time the first time you use it, walk away and take your data with you.