Yes, some companies tell you on their website when to expect the next round of shop postings, but most do not. I find that most of my companies post the last week of the month or the first week. But there are exceptions. I have learned over time which ones post about every two weeks, which ones seem to post different shops at different times of the month (leading to new postings every few days), which ones seem to post close to midnight on Saturday night, etc. etc. Experience is the best teacher. I generally make notes on my shop log so when it is the 18th of the month I know it is important to closely watch this or that company and on the 23rd I need to start watching those companies and the 5th this company usually posts, etc. And once they have posted, I know that a weekly check for work other shoppers may have cancelled is all I need to do.