The Rosh explains that since the ending time corresponds with the Hakravas ha'Tamid, it may be assumed that the starting time also corresponds to the times of the Tamid. The Ma'adanei Yom Tov clarifies that if the Mishnah would state only the starting time, we would mistakenly have thought that there is no duration; by stating the ending time we can infer that both the beginning and the ending times for the Tefilos are parallel to the times of the Tamid. The same is true for Tefilas Minchah and the afternoon Tamid.

Dov Zupnik