When McNulty/Prez first step out to pick up Chinese food for the others, it is daytime. The scene then cuts back and forth between story lines such as Stringer/Avon where it is daytime, back to McNulty/Prez still picking up Chinese but now it's night, over to Daniels/Pearlman's meeting with the Feds during the daytime, then finally back to the Chinese food run still at night. (It could have just been a really long food run).