Upvote:3
The standard published timescale is 15 working days, unless you are applying from a location where a priority application is possible (which does not guarantee a quicker response, however Priority visa converted into standard visa) You can check the timescale for your location via https://www.gov.uk/visa-processing-times. You can of course apply at short notice but you risk not getting the decision in time if your departure date is not flexible.