In terms on flights, 54 days ago was a magic number but this is changed over time. Now, the prices are totally fluctuating depending upon various factors such as season, time of flight, demands, destinations tourism demands and lot others. So now there is no such fixed time to book, however mon to wed is the best time to book. Same applies in terms of hotels. Also avoid over searching for tickets, it leads to cache traffic which companies utilize to inflate prices.