The Sessions could not be earlier than 1929, given that the patent, US 1700506, was granted January 29, 1929.
The Seth Thomas is similar to one called the Roslyn, shown in Tran Duy Ly's book on Seth Thomas clocks from the 1904 and 1906 catalogues. However, it is not an exact match for the catalogue illustrations. Here is a link to a picture of the Roslyn. Nonetheless, since your clock has what Seth Thomas called its No. 89 movement, that would place it sometime after 1900. So, 1904-06 might, I suppose, be a good date range.