I do not have any direct evidence regarding the time control for Leningrad 1934.
However a time control at the 37th move was used in Moscow 1935 (won by Botvinnik and Flohr ahead of Lasker and Capablanca).
6. Time for thinking: for the first 37 moves - 2 1/2 hours, for every 15 moves after that - one hour (with accumulation of time). Thus a control check of the chess clocks will take place after the 37th move, the 52nd, the 67th, the 82nd and so on.
Source: page 24 of Moscow 1935 International Chess Tournament (Translated by Jimmy Adams and Sarah Hurst: Caissa Editions, Yorklyn, DE 1998). From the Section "Programme of the Second Moscow International Chess Tournament" at pages 23-25.
Moscow 1936 (won by Capablanca ahead of Botvinnik) had a probably more usual first time limit at the 40th move.
Thinking time: for the first 40 moves - 2 1/2 hours, for each subsequent 16 moves - 1 hour [togther (sic) with the accumulated time]. Thus the control shown on the chess clocks falls after the 40th move, 56th, the 72nd, etc.
Source: page 6 of Moscow 1936 International Chess Tournament (Translated and edited by Jimmy Adams: Caissa Editions, Yorklyn, DE 1988). From the Section "Programme of the Third Moscow International Chess Tournament at pages 5-6.