Check the sample rate configuration in the software
you are using. Older Apple products used a hardware sample rate of 44.1 ksps, whereas newer Apple products all seem to use a hardware audio sample rate of 48k (or a multiple thereof).
Dr Warren Pratt, NR0V, introduced low-latency FIR filters to the 2018 SDR Academy. Dr Pratt reminded the audience that mimimum phase FIR filters deliver much lower latency than linear phase filters and opined that ease of design has driven the persistence of linear phase filters. I have observed a dramatic reduction in latency by switching to Dr Pratt's WDSP ...
The answer is that the SDR hardware devices are all very different, so is the optimization quality of the SDR code. So one pretty much needs to calibrate for their specific setup: device, current method of connection, OS, and software running.
I find network latency between the SDR hardware server and the software client to be one of the biggest variables, ...
If you want to transmit Morse code, or just to learn more about flowgraphs, you might be interested in https://github.com/duggabe/gr-morse-code-gen
Note: if you change the output rate to something other than 48khz, you will need to change the parameter calculations as well.
It's difficult to give an exact number, because the overall latency involves at least:
Processing of the signal on the given SDR
Transferring data over USB 2.0 / USB 3.0 / PCIe (depending on what is used)
Latencies on USB controllers on both SDR and PC (+ USB hubs, if used)
Latency caused by other USB devices (keyboard, touchpad, webcam, ...) on the bus. ...