The implementation of Seamus uses indexes instead of real dates, where the last value on Friday +1 is the first value on Monday.

Of course then you need a different way how to map values to date time strings for the tick values and you will have the problem that the ticks are not necessarily aligned to date time units.

Another option might be to implement a special type of QwtTransform, that tries to eliminate periods, where no trading happens. I'm not sure how to find such an algo, but the scaleengine example shows how to implement a scale where a special interval is expanded ( "At 400" ). In a a similar way intervals can be shrunk.

Uwe