IMO LE is doing their job by asking for anyone that can be a potential witness to come forward. They have no idea what the witnesses may or may not say. They are using the timeline of Sunday to Monday because they have to go back to the actual last KNOWN and VERIFIED sighting of Dylan. In broadening the time frame, they are looking at all possible avenues.
When a tip comes in, they (LE) has an obligation to review it, some are so off the wall that they can immediately be discounted. Depending on how the tip was called in, LE could just pass by it not knowing what the tipster is actually adding to the investigation.
This is John Doe, please give me a call at 234-5678, Thank you LE calls the number, leaves a message and the guy never calls back. Or his mailbox is full and cant receive a message.
In this case, they received a tip, spoke with the tipster and are following up on it. Nothing more, nothing less.
Imagine what would happen during a criminal trial:
Defense Attorney: Mr. Bender, do you remember receiving a tip about a 45-50 yo Hispanic male acting suspiciously on the morning of November 19, 2012
Bender, Yes I remember that tip
Defense Attorney, Did you ever try to locate this 45-50 yo Hispanic male?
Bender, No we did not
Defense Attorney, Why not?
Bender, Well it came in three months in to the investigation and we just didnt think it was important to find this individual.
Ok, so now the police have given reasonable doubt to every jury member on the panel. LE did not eliminate everyone except the defendant. Tunnel vision is not investigating. I dont believe that it matters one bit that this tip just came in, I do believe that it matters one bit that LE is asking for this individual to come forward. IF there is ever a trial, LE can say with 10% confidence that they received a tip on a person that may be a witness and LE did everything in their power to find this witness.