The Rogatchover, in Tzafnas Paneach (Hilchos Kilayim 9:5) suggests a proof that semicha does not have to be performed by day. He says that regarding a korban of partners, in which each partner must perform semicha, one partner’s semicha will obviously not be performed immediately before the shechitah. Therefore, in this case, whereby the semicha does not have to be performed immediately before the shechitah, the semicha should be permitted to be performed at night. Accordingly, semicha would not be considered a mitzvas assei she’hazman gramma.
Two points: 1) According to the answer that we just concluded from the Acharonim, namely that we derive from a drasha that semicha must be performed during the day, even if it were not being performed immediately before the shechitah it would have to be performed during the day.
2) I would suggest that when partners simultaneously perform semicha on the animal, it is considered that each semicha was performed immediately before the shechitah. Since they are all required to perform the semicha, it is considered to be one long, uninterrupted semicha. Thus semicha is always performed immediately before shechitah, and as such is considered a mitzvas assei she’hazman gramma.