Dates in OQL not finding last day of the date range.

I want to limit a Report to a specific date range, e.g 1st June - 30th June 2016.

I have tried both the following snippets of code and they both have the same issue:

AND devs.ContractDate IN $datetest

... and devs.ContractDate >= RANGEBEGIN($datetest) AND devs.ContractDate <= RANGEEND($datetest)

Data for 30th June 2016, is not included.

The RangeEnd ($dateTest) is set to the start of day, so any data with dates equal to $dateTest are not extracted because the time part of devs.ContractDate is greater than the time part of RANGEEND($datetest).

As OQL does not allow date calculations to add 1 day, there is not a way of making the OQL work, except to tell the users to set the end date as 1 day later (which is not user friendly).

Does anyone know how to perform calculations within the Where clause on date / time?