The surface of Lake Baikal is generally frozen from early January until May or June (~5 months). Typical ice thicknesses are around 1 m, but some small hills of ice can form and lead to local thicknesses of more than 2 m.

( More about Lake Baikal that is unrelated to this question.)

According to Wikipedia, it's 4-5 months (January through May), and is typically between 0.5 m and 1.4 m thick.

Lake Baikal in Siberia is the oldest and deepest freshwater lake in the world. It is frozen for up to five months a year and its ice is so thick cars often drive across it. The cold temperatures mean "ice waves" form on the shoreline. Oct 24, 2016

Lake Baikal shoreline.

How thick is the ice on Lake Baikal? 0.5 to 1.4 m.

During the winter and spring, the surface freezes for about 4–5 months; from early January to early May–June (latest in the north), the lake surface is covered in ice. On average, the ice reaches a thickness of 0.5 to 1.4 m (1.6–4.6 ft), but in some places with hummocks, it can be more than 2 m (6.6 ft).

Lake Baikal