i don't think you have to get the coffees at any special time, except for the one in Dali. *don't forget to give the old man Morrid the coffee before you go to Terra.

1) one of the coffees is in Eiko's kitchen at Madain Sari.

2) one of the coffees is near the Chocobo Forest (the first one); look for a gate arch near the forest. *the coffee is next to some water you can drink to restore HP/MP.

3) one of the coffees is behind the windmill in Dali. *you can only get it if you find the Mayor's Key. *the best time to get the Mayor's Key is during the Treno Card Tournament. *sneak into the Mayor's house and search the desk 3 times, then search the stove to get the key. *use the key on the locked door in the windmill to find a Chocobo. *on the far right of the Chocobo's stable, you'll find a chest full of money. *search the chest again to find the coffee underneath it.