It can be a few days after the discharge starts to show. Have you been taking her temperature? A significant drop is a good indication.

Some bitches don't show many otuward signs ata ll. My girl stopped eating and drinking on day 59 (I had to syringe water into her mouth!) with some very mild panting, then promptly ate her breakfast on day 60. Her waters did break on the afternoon of day 60 though at 3.30, and our first pup was born just after 7pm.

No digging, no restlessness. I don't think anyone other than me woudl have noticed she was in labour. I even rang the vet who didn't think she was.