So ‘wyt ti’n gwneud rhywbeth?’ is ‘are you doing something?’ in the present, and ‘oeddet ti’n gwneud rhywbeth’ is ‘were you doing something?’ - hope this helps…
I think that the northern SSIW course in general uses the unabbreviated versions for those – oeddet ti’n rather than o’t ti’n, “oedden ni’n” rather than o’n ni’n – doesn’t it? Iestyn’s a bit more eager to move on in the sentence and uses the shorter versions.