Disclaimer:
Please Note that the spawn times are estimated based on the “Knowledge” that Field Boss (Bheg, Dim, Red Nose, Mudster) spawn between 10-19 hours and World Bosses (Kzarka) spawn between 8-12 hours. These are rounded values due to the ~roughly 20% increased Spawn Rate with the Patch from 05/13/2016 (Patchnotes here).
Until now my predictions worked fine but please keep in mind that even I can do some wrong calculations. In addition I am not able to do every single world boss and there might be some unconfirmed Timers listed here – however these timers are marked as unconfirmed and they should still spawn within that timeframe as I add early/latest spawn to them as well.

I will do my very best to keep this list updated as good as possible!

EU Servers – Timer is in CET

Field & World Boss Timer EU Server 100% IHA confirmed Timer

NA Servers – Timer is in EST

Field & World Boss Timer NA Server 100% IHA confirmed Timer

SA Servers – Timer is in BRT

Field & World Boss Timer SA Server 100% IHA confirmed Timer

MENA Servers – Timer is in AST

Field & World Boss Timer MENA Server 100% IHA confirmed Timer

SEA Servers – Timer is in SGT

Field & World Boss Timer SEA Server 100% IHA confirmed Timer