Since I think this is going to come up at some point soon I decided to try to get a timeline of the first episode of the events related to Orkarin, Kurisu, and Mayuri.

Approximate times.

1:55 Okarin hears a crashing sound from the roof and goes to investigate.

2:11 Okarin sees the time machine on the roof. Person (female) wearing half gloves raises arms and makes a chopping motion. She seems to be running toward the machine rather than coming from it.

5:00 Kurisu tells Okarin that he talked to her 15 minutes before

6:35 Orkarin recieves message that has a snowy video (can't read the Japanese)
Mayuri says she texted him but the message doesn't seem to be from her.

7:27 Orkarin hears a scream that appears to be his voice.

8:02 Okarin finds Kurisu dead on the eighth floor

9:17 Okarin sends e-mail to Daru and experiences a time shift (he finds out that it went two weeks into the past).

10:26 Sees the "satellite" crashed on the roof (if it's the time machine it looks a lot larger than it did the first time)

Mayuri tells Okarin that the reason they went to the building was to see the crashed "satellite" not to see the Doctor Nakabachi's talk which didn't occur because he was scared off by the crash.