Set annotation X1 and X2 to be in between major grid units

I use a simple box annotation to highlight a section candlesticks on a chart. Currently I only see how to set this annotation X1 and X2 to Major grid units (ie 1,2,3,4,5). Since I would like to have this box annotation fully highlight only the desired candlesticks, is there a way to offset this X1 and X2 position by 0.5 so that it would include only (and fully) the desired candles? Apologies if I have missed this in the docs somewhere but I have been unable to find anything to accomplish this.

EDIT: For my x axis I am using a CategoryDateTimeAxis

Thank you.