Let's say the standard delay is five seconds. So the source is five seconds ahead of real time.
The signal destined for FM is delayed by five seconds before it goes to the transmitter. So it's real-time.
The signal destined for DAB is transmitted immediately. The DAB receiver delays the digital signal, using a FIFO buffer, so that the audio is output five seconds after reception. As you've probably worked out by now, I'm not an engineer, so these figures are suspect, but for example: if the decoder takes 2 seconds, the signal must be delayed by 3 seconds before decoding, which if the signal is 720kbps (I wish) would require a buffer of 270kB. Different decoders that work at different speeds would require a different size of buffer.
I've not taken DTTV and DSAT into account because I've no idea what they are: are they radio? My only experience is with FM, DAB, and Freeview.