How often was the Ketores burned during the eight days of the Milu'im?
Rashi: Twice daily, in the morning and in the afternoon. 1
As the Pasuk specified in 30:7 (Rashi).
Who burned the Ketores?
Ramban: Moshe, during the first seven days - even though he was not specifically commanded to do so, 1 he understood that he should, from the Avodos that he was commanded to perform. 2 Once Aharon and his sons began performing the Avodah - on the eighth day, burning the Ketores was confined to them. 3
See Pasuk 5 (Ramban). As a matter of fact, he was not commanded to bring the Korbanos either - only to arrange the loaves on the Shulchan and to kindle the Menorah (See Pasuk 4).
Refer to 40:27:1:1* and refer to 40:29:1:1*. It is also possible that the Torah hinted that he should, when it wrote above in Pasuk 5 "Venasata es Mizbach ha'Zahav li'Ketores" (implying that Moshe should burn it immediately [Ramban]).
As the Pasuk specifically stated in 30:7, 8 (Ramban).