Today I davened mincha close to Shkia and realised that the chazaras ha shas would finish after Shkia and therefore tachunun would not be said. I said tachunun after my silent amida before chazaras ha shas started so not to miss it.
Was this the right thing to do?
We are allowed to say tachanun after shkia, even though it is bein hashmashos, it is permitted. Therefore technically you didn’t have to do that, however it is still a correct thing to do, as there are those that say not to say tachanun during bein hashmashos( see sources). This is the minhag in Yerushalayim.
O:CH 131-3, MG:A ibid 9 (see Beer Heitiv 9) Taz ibid 8, M:B 17. Tefilah Khilchso 18-34 in the name of R’ Eliyashiv zt”l, Aleihu Lo Yibol pg. 298 in the name of R’ S. Z. Auerbach zt”l, that this is the minhag in Yerushalayim. Others say that this is the minhag in the whole E. Yisroel, Teshuvos Vhanhagos 3-53, and the minhag of many chasidishe people.