As a Deputy US Marshal on a Fugitive Task Force, who serves warrants every day, I'll give you my opinion..
I think you should probably defer to the thought that any real-officers are going to be very noisy, and most often work during the normal 8-5 working hours timeframe. I don't think you could ever expect warrant service after 9:00 pm, or before 5:00...
The officers serving the warrant could be from the US Marshals, DEA, ATF and the local PD may know nothing about the warrant. As often as we ask for the local PD to assist us, we also serve warrants on our own and the local PD has no idea we even came to work today.
There is no "hotline" you can call to determine if they are real cops or not.
The standard protocol (except for rare no-knock warrants) is to knock and announce "POLICE, OR "POLICE WITH A WARRANT" very loudly, then wait a "reasonable" amount of time that it would take for someone to answer the door..in most cases 30 seconds to 1 minute...maybe less depending on the agency, the officers, or the person/property the warrant is for. If they are worried that some child porn vendor might erase his HD, or the meth is going to get flushed, that waiting period at the front door may be very brief, it only has to be long enough to be "reasonable", unless there is exigency because the officers fear that evidence is being destroyed etc..
If no answer, to door gets kicked/rammed...
I know this is a pro-gun, pro-defense-of-my-castle, right-to-bear-arms website (so am I for the record), however, you better not be standing there with your GLOCKTALK COMMEMORATIVE GLOCK 17 in your hand when they come through, because they WILL NOT wait for you to raise it, having it in your hand is justifiable "intent" to shoot you and ask questions later and the courts will lean in their favor.
Officers are trained nowadays, not to wait until the perp raises the gun in their direction. If I'm doing a felony traffic stop and the driver grabs a gun from the glovebox, I'm not waiting until I can see down his barrel before I start shooting. The driver reaching for the gun displays "intent", and again, the court will lean in the officers' "good faith" assertion that the driver displayed "intent".
Same thing goes when serving warrants. If we knock and announce, and then kick the door and on the other side is a guy with a gun in his hand, he's most likely getting shot right there, whether he raises it or not.
Just some thoughts....