Geneva is 4.5 hours behind Colombo
Best overlap: 1:00 PM to 6:00 PM in Colombo is 8:30 AM to 1:30 PM in Geneva.
Aim for 1:00 PM to 6:00 PM Colombo time — that's 8:30 AM to 1:30 PM over in Geneva. With 5 hours of overlap, 1:00 PM in Colombo (8:30 AM in Geneva) is a comfortable, repeatable slot for both sides. These times hold for most of the year, but Geneva's daylight saving (which Colombo doesn't use) shifts them by an hour twice annually.