Unless the laws have changed in the last few years, to use an IP address to get an exact address of the modem, you will need a warrant to get the suspect’s ip address in some instances, unless someone who already has it is willing to share it. After that, the LE Officer needs to subpoena the isp, (like aol or Yahoo or whoever is the internet provider) to get the home address. This usually takes time to get the info, but in cases of an emergency, most internet service providers will respond fairly quickly. Getting only the town or city is much easier.
The time factor comes into play when trying to access a person’s cellphone calls and especially text messages. Some cellphone providers take their time in some instances, but if LE uses an order from a Judge requesting to fast track the information, that can speed up getting the information. Best way to speed up getting the information is to have the phone in hand. Even if they remove the SIM card, a lot of information can still be pulled from the phone.