There is a time period when two sessions are open at the same time and overlap:

Tokyo and London Session: From 8:00 AM to 9:00 AM.
London and New York Session: From 1:00 PM to 5:00 PM.
Sydney and Tokyo Session: From 00:00 AM to 7:00 AM.

These are peak hours of trading activity. The most liquid overlap sessions are London and New York. This is when the most trades are made making it an excellent time for active market participants. Based on the analysis of the volatility of different currency pairs, Tuesday and Wednesdays are considered to be the best days of the week to make trades. In terms of the seasons of the year, we should first mention December. Before the holiday season starts, the volatility is quite high. However, after the 20th of December and until mid-January, there is a period of inactivity in the market. Once the holidays are over, things go back to normal. Forex remains very active until the end of summer, or rather, until July-August when loads of people go on vacation with their families. In September, the trading intensifies again with peak activity lasting from mid-October to mid-December.