Assuming you're on google.com/flights, I'm fairly sure that using a VPN, changing your IP, flushing your cookies... none of that should change the availability

Assuming you're on google.com/flights, I'm fairly sure that using a VPN, changing your IP, flushing your cookies... none of that should change the availability and pricing you see on Flights. And no, don't bother trying to time your bookings. It's kinda like the stock market; trying to beat the market, er, optimize your flights purchase time is likely to lead to sorrow and regret. From the research our Google Flights team did recently, we found that if you wait a week, on average you're gonna pay more for the same flight. And no, we didn't see any universal discount on Tuesdays, either ;)