Related for Pesachim 11:17

הני שלשים יום מאי עבידתייהו כדתניא שואלין ודורשין בהלכות הפסח קודם הפסח שלשים יום ר' שמעון בן גמליאל אומר שתי שבתות מאי טעמא דתנא קמא

For Raba said: If one turns his house into a granary<span class="x" onmousemove="('comment',' I.e.,he stores provisions in it, and under them lies leaven.');">²⁵</span> before thirty days [prior to the Passover], he is not bound to remove [the leaven];<span class="x" onmousemove="('comment',' By being buried under his provisions it is as though it were removed.');">²⁶</span> if within thirty days, he is bound to remove it;<span class="x" onmousemove="('comment',' Because the obligation to remove it becomes operative in this period, and one cannot remove it thus at the very outset.');">²⁷</span> and even before thirty days too, we said this only when it is not his intention to clear it [the store of provisions] away; but if his intention is to clear it away, even before thirty days too he is bound to remove it What business have these thirty days?<span class="x" onmousemove="('comment',' Why is the matter dependent on this period?');">²⁸</span> - As it was taught: Questions are asked and lectures are given on the laws of Passover for thirty days before Passover. R'Simeon B'Gamaliel said: Two weeks. What is the reason of the first Tanna?

Tosefta Megillah