Surry Hills Shopping Village (corner of Cleveland and Crown streets) parking lot is free and untimed.
It is a genuine 15-20 min walk, so you can get closer, but you can pick up a kebab or a curry on the way - that's what I do. And if you go the back way you'll avoid the hell that is Cleveland St traffic.
Park next door at Sydney Girls High ie ignore the first guy trying to wave you in off Cleveland St, go to the next guy. Its not as big and you generally get out quicker especially if you leave right on fulltime.