69:6 If the hour is late and it's getting close to nightfall, the shaliach tzibbur starts to recite Shemoneh Esrei out loud immediately after finishing Kaddish. The congregation does not recite the silent prayer at that time. Rather, they listen and respond to the shaliach tzibbur until the end of the bracha "Ha(k)Eil HaKadosh." After responding amen to that bracha, the congregation begins the silent Shemoneh Esrei. If it's very late and there's not even time to wait until after the shaliach tzibbur says "Ha(k)Eil HaKadosh" because they will not be able to finish their individual Shemoneh Esreis before nightfall, they may then recite Shemoneh Esrei silently, word by word, along with the shaliach tzibbur until "Ha(k)Eil HaKadosh." It is preferable, if at all possible, to have at least one person responding to the shaliach tzibbur's recitation of the brachos.
69:7 If a person came to the shul and found the congregation saying Shemoneh Esrei, he should say it with them and recite Ashrei afterwards. If he can't finish the Shemoneh Esrei before the shaliach tzibbur reaches Kedusha, and if waiting until after the shaliach tzibbur has finished saying Shemoneh Esrei and Kaddish would cause him to miss the time for saying Mincha altogether, he should should wait for the repetition of Shemoneh Esrei and recite it silently along with the shaliach tzibbur. He should even say Kedusha along with the shaliach tzibbur, and he should try to complete the brachos of "Ha(k)Eil HaKadosh" and "Shomeiah Tefillah" along with him. He should also say Modim along with the shaliach tzibbur so that he ends up bowing at the same time as the congregation. The only deviation one should make from the shaliach tzibbur in such a case is if it should happen to occur on a public fast day. If that should happen, the individual should say the version of Aneinu that appears in Shema Koleinu (like he normally would) and not the version that the shaliach tzibbur recites after Goeil Yisroel. Similarly, if one wants to daven Maariv with the congregation but waiting until after the repetition of Shemoneh Esrei to say Mincha would cause him to have to say Maariv alone, he should daven Mincha silently along with the repetition. If he arrived shortly before Kedusha, he should wait until after the shaliach tzibbur says "Ha(k)Eil HaKadosh," say amen to the bracha, and then daven on his own. Even though one loses the opportunity to respond amen after the key brachos of Shomeiah Tefillah and Modim, this is still the best available course of action, since the alternative is not to daven Maariv with a minyan. (Bi’ur Halacha 109:1 s.v. L’kedusha oh l’kaddish cites the Pri Megadim that answering these two brachos takes priority over davening with a minyan.) This is especially so if the time for Mincha is almost gone.