The Sanskrit word अवयव is used here. Yaska in nirukta 2:27 explain it as one who move in it's way. It can be anything. Many interpret it as Ray's.
Rigved 1:105:9:- Where those seven rays of sun are shining, thence my home and family extend.This Tṛta Āptya knoweth well, and speaketh out for brotherhood. Mark this my woe, ye Earth and Heaven.
The verse cleared that Hindus knew about sun's seven Ray's.
##Is God Surya or those horses in any way related to kala(time)?
Atharvaved 13:2:39 says that sun is reference of time.
[1][1]
It is a fact that sun decides the day, night, months, seasons and years.
##Who is the God sitting infront of Surya, controlling those horses with stick? He is Aruna, Elder brother of garuna and son of safe Kashyap and Vinata. He became charioter of sun because of their father's boon.
##What is that stick called? Scriptures have know reference about stick. Some pictures show that stick or some not.