MB4 234b: What Happens if the Eruv Chatzeros Gets Diminished Below the Minimum Shiur? (368:4-5)

If the Eruv Chatzerot food becomes diminished below the minimum shiur as long as the minimum shiur was there for bein hashmashot of the first Shabbos as long as there is some left.

If the food used for the eruv spoils or otherwise becomes inedible a new eruv chatzerot is needed.

Why matzah is usually used.

What if the eruv food is not edible for halachic reasons? (e.g. chodosh, matzah on Shabbos-Erev Pesach)

From when on Shabbos can the eruv chatzerot be used?