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The 9150 is a twin tuner model. That means it can receive 2 ‘multiplexes’ at once, allowing picture-in-picture, to record two programmes at once or watch one and record another.
A ‘multiplex’ is a single digital transmission channel that can carry several individual TV or radio programmes at once. E.g. there is a multiplex that carries most of the BBC channels. If you are recording two programmes you will be able to watch a third, but only if that programme is on the same multiplex as either of the recording programmes.
There are 5 standard definition freeview multiplexes, and these carry all SD TV and radio transmissions for Freeview. See our FAQ thread here for more information.
With regard to your second question, are you using accurate recording, or do you have the ‘start early’ and ‘end late’ times set?