Posting in advance (by 1-2 weeks) ensures that you are matched with the most suitable Stinters and maximises your chances of getting Stinters in your Team / people have worked with you before.
As your busy periods tend to fall within the same time frames week-by-week, you will be able to build up a regular schedule with your favourite Stinters, as their timetables generally coincide with the times you need them.
Posting in advance ensures that these Stinters are able to prioritise and accept your Stints first.