All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
If what is meant is prolonging the Madd (prolongation) of Alif that is after the letter Laam of the name Allaah, then it is to be prolonged a normal Madd, i.e. for only two Harakahs (beats: each beat is equal to the duration of moving one's finger in or out moderately). Exaggeration of Madd for more than two Harakahs does not invalidate the prayer but it is not legislated.
As for the word Akbar, it has no Alif to be prolonged. Also, prolonging the Hamzah of Akbar and adding Alif between the letters Baa’ and Raa’ is not correct; rather, it invalidates prayer if it occurs in Takbeeratul Ihraam (i.e. the first Takbeer in prayer) as stated by the jurists.
Allaah Knows best.