One may only roast meat, an onion, or an egg if there remains sufficient time so that they could be roasted while it is still day. One may only place dough to bake into bread in the oven on Shabbat eve at nightfall, and may only place a cake on the coals, if there is time enough that the surface of this cake or bread will form a crust while it is still day. Rabbi Eliezer says: Enough time so that its bottom crust should harden, which takes less time. However in a case that is an exception, one may, ab initio, lower the Paschal lamb into the oven on Shabbat eve at nightfall, so that its roasting is completed on Shabbat if Passover eve coincides with Shabbat eve. And one may, ab initio, kindle the fire in the bonfire of the Chamber of the Hearth in the Temple on Shabbat eve, adjacent to the start of Shabbat, and allow the fire to spread afterward throughout all the wood in the bonfire.
The Chamber of the Hearth was a large room along the northern wall of the Temple courtyard. Half of it was in the courtyard and half was considered to be outside the Temple. The Chamber of the Hearth was built with a dome and had a great bonfire for the purpose of warming the priests returning from service or emerging from immersion.
Since the priests worked barefoot, wore light clothing, no additional layers of clothing could be added, and the Temple was mostly without a roof, leaving them exposed to rain and wind, the priests would avail themselves of this chamber to warm themselves. Although this was not part of the Temple service, it was part of the arrangements for the benefit of the priests. At the same time, there is the principle that rabbinic decrees were not implemented in the Temple, and the Temple area was governed exclusively by Torah law, without additional rabbinic restrictions and fences.