I'm referring here to the CX5's general (motor) firmware not specifically to any entertainment firmware etc. A couple of weeks back my own 2015 CX5 went in for an oil + filter change (mid service at my own request). At this time it was noticed that the vehicle needed a firmware update which was then undertaken. After almost sixty minutes the technician came back to me and stated that there was obviously a bad internet connection between the workshop and Mazda and that they were unable to install the firmware. Subsequently a further appointment was made for this to be executed. However, no sooner had a driven away from the forecourt than the dashboard lit up in Blackpool illuminations fashion with just about every warning symbol one can possibly imagine lighting up. This prompted an immediate U-turn with the car returning to the service bay.
Less than 10 minutes later the vehicle was returned to me with the technician stating "all sorted" and with the presumption being that whilst the firmware upgrade had been unsuccessful overall certain aspects of it had installed and were now mixing with the old firmware. In short - chaos. To get around the problem of the bad internet connection between the workshop and Mazda the technician used his own mobile phone to download and install the newer firmware and as stated, in a very short period of time the problem was solved and the newer firmware installed.
It would appear, therefore, that reports of firmware updates taking excessively long can only be put down to workshop technicians executing multiple jobs on different vehicles at once as in my case it has been shown updates can be executed in a very short period of time.