That's *if* they know the time of death yet. We could easily assume they don't at the time of his arrest, since Bellick's questioning is still the day of (or maybe day after) Geary's death. Also unknown is when Bellick came in to the hospital. It's conceivable Bellick came in an hour or 2 before Geary did, which would make the timelines work.
Now, if Bellick gets convicted of killing Geary, then I'd have some problems (i.e. no prints of Bellick found at the scene, the time of the voicemail & time of death, lack of a murder weapon, etc.)