The sentence in question is:
Idhevāhaṃ sāvatthiyaṃ komudiṃ cātumāsiniṃ āgamessāmī”ti
B. Ñaṇamoli / B. Bodhi:
I shall wait here at Sāvatthī for the Komudī full moon of the fourth month.
B. Ānandajoti:
I will be right here at Sāvatthī until the fourth month of Komudī comes.
B. Thanissaro:
I will remain right here at Savatthi [for another month] through the ‘White Water-lily’ Month, the fourth month of the rains
M. Cone:
āgacchati […] comes, comes near; comes back, returns; reaches, attains; is recorded, is handed down by tradition […] fut. 3 sg. (a) āgamissati […] āgamissati is a not uncommon wr for āgamessati […]
I’m lost here - where do they get the sense of waiting at Sāvatthī until Komudī? Does it not actually mean: ‘I will come back at Komudī’ ?