The sunnah is for the takbeer to be in conjunction with the movement, such that one begins the takbeer with the beginning of the movement. The daleel (evidence) for this is the hadith of Abu Hurairah in which was said:
Abu Huraira used to say takbeer in all the prayers, compulsory and optional, ... He used to say takbeer when standing for prayer and when bowing; then he would say, "Sami'allahu li-man hamida," and before prostrating he would say "Rabbana walaka-l-hamd." Then he would say takbeer when prostrating and when raising his head from the prostration, then another takbeer when prostrating (for the second time), and when raising his head from the prostration. He also would say the takbeer when standing from the second raka'a. He used to do the same in every raka'a until he completed the prayer. On completion of the prayer, he would say, "By Him in Whose Hands my soul is! No doubt my prayer is closer to that of Allah's messenger than yours, and this was his prayer until he left this world." (al-Bukhari)
The scholars have have understood from the Arabic word "heena" used in the hadith (translated here as "when") that the beginning of the takbeer should be in conjunction with the beginning of the movement.
Note that some scholars have recommended that the saying of takbeer should extend throughout the movement, from when it starts until it ends; however, there is no daleel (evidence) for this.
Sheikh Muhammed Salih Al-Munajjid