No, there were no dates formally agreed upon.
Some historians (ref. Victor Suvorov's "Icebreaker") speculate that there is indirect evidence suggesting that along with the "Communazi Pact", the specific date of joint German/Russian invasion on 1 September was agreed, but Suvorov did not provide with any documental evidence.
Moreover, it is known that German invasion to Poland was postponed at least once. German plan was to start the invasion on 26 August, but a day before, on 25 August, Britain entered into a defense pact with Poland, forcing Hitler to postpone the invasion of Poland to 1 September.
The full text of the secret protocol is short enough to be quoted here.
Article I. In the event of a territorial and political rearrangement in the areas belonging to the Baltic States (Finland, Estonia, Latvia, Lithuania), the northern boundary of Lithuania shall represent the boundary of the spheres of influence of Germany and U.S.S.R. In this connection the interest of Lithuania in the Vilna area is recognized by each party.
Article II. In the event of a territorial and political rearrangement of the areas belonging to the Polish state, the spheres of influence of Germany and the U.S.S.R. shall be bounded approximately by the line of the rivers Narev, Vistula and San.
The question of whether the interests of both parties make desirable the maintenance of an independent Polish States and how such a state should be bounded can only be definitely determined in the course of further political developments.
In any event both Governments will resolve this question by means of a friendly agreement.
Article III. With regard to Southeastern Europe attention is called by the Soviet side to its interest in Bessarabia. The German side declares its complete political disinteredness in these areas.
Article IV. This protocol shall be treated by both parties as strictly secret.
Moscow, August 23, 1939.
For the Government of the German Reich v. Ribbentrop
Plenipotentiary of the Government of the U.S.S.R. V. Molotov
(English translation from here)