As I read it...
If, as of December 31, 1934, no signatory has declared it's intention to leave the treaty, then as of Dec 31, 1936 the treaty will automatically continue in force until it will abruptly terminate for all parties two years after notice is finally given.
Example (if I have it right):
Dec 31, 1934, pretend all powers are still in, no one has declared their intention to exit.
August 10, 1935, Lichtenstein (who for some reason joined) declares it will leave.
Prior to August 10, 1936 the Contracting powers would be bound to meet in conference(1)
Dec 31, 1936 As no powers declared exit by Dec 31, 1934 the treaty continues in force
August 10, 1937 Lichtenstein's declaration takes effect, the treaty is canceled for all parties.
(1) This of course was why the San Francisco conference was called, but some contracting powers had already fully withdrawn, and not all contracting powers bothered to attend.