When one blows Shofar on Rosh HaShana, how much time is the Tekia supposed to take in order to be Yotzei the Mitzva?
Source Shulchan Aruch HaRav 590:7
As to how long the Shevarim and the Teruah have to be, it depends on the definition of the Teruah. It is 3 Yevavot (not quite sure how to translate that, see Talmud Rosh Hashanah 33B), and according to some opinions a Yevava is 1 staccato blast, and according to others it is 3 staccato blasts.
A Shevarim need to last as long as a Teruah.
Therefore, according to the first opinion:
According to the second opinion:
Source: Shulchan Aruch HaRav 590:4-6
LeHalacha, The Shulchan Aruch HaRav (590:7) says that one should LeChatchila follow the second opinion. Bedieved he fulfills his obligation if he followed the first opinion. If he mixed up the two opinions in such a way that he would not have fulfilled it according to either of the two opinions he must redo it.