Reading an ECU depends on the vehicle. Some can be done via OBD and some I need to remove the ECU and connect to it directly in which case removing and refitting takes longer.
For ECUs that can be connected via OBD anywhere from 45minutes - 1.5hrs depending on read and write times. For removal usually 1hr - 2hrs. Where there is an Adblue delete, sometimes longer as some vehicles require the Adblue module and/or pump disconnecting.

It may also take longer where further adjustments to files is required. This is rare, but some vehicles, mostly Fords sometimes require adjustments of Checksums if the vehicle rejects the modification. Some Peugeots also need the vehicle locking and leaving for the ECUs to power down before starting the vehicle. All of which is very standard and of no concern.

In short, NO!
Most ECUs can, many cannot. Manufacturers often LOCK ECUs. Many have a workaround so this isn't an issue, but some don't. For example, Transit Custom SID212 hasn't been cracked by any tool supplier yet.

Also, different tool manufacturers have cracked different ECUs, so where my tool will not access your ECU but another tool will, I will refer you to another mapping supplier that might be able to assist instead.