Rukūʿ (Arabic: رُكوع) refers to two things in Islam.
1. RUKU is a step of prayer in Islam where someone bows down (places hands on knees) and then goes to Sajdah (placing forehead on the ground).
If you proceed to Rukoo' before the Imam of Jama'ah or Jum'ah thinking that he is in Rukoo', you need to stand back and return to Rukoo' then follow the Imam. Your Salaah will be valid.
as salam alaikum
in the mentioned case, you should go back in the standing position (qiyam) and continue to follow the Imam.
With prayers for your success.
It is recommended to say Subhanallah one time or more before Dhikr of Rokoo' and Dhikr of Sojood. If you say Subhanallah three times, it will be like saying Dhikr of Rokoo' or Sojood one time. Repeating Dhikr is recommended either three times or five or seven or nine or more odds.
There is no limit of number of times we can repeat he Thikr or Rokoo' or Sojood. It is recommended to repeat it 3 or 5 or 7 or more in odd times.
The term قیام متصل برکوع means pausing for a moment after recitation before going to the ruku.
According to the office Ayatullah Sistani (may Allah prolong his life)
1) It's wajib
2) if one goes to the ruku without the mentioned pause, they have to return back to standing position (qiyam) pause for moment then perform the ruku.
Also refer to the following issue will be helpful to you
969. If a person forgets to perform Ruku, and sits down after reciting Hamd and Surah, and then remembers that he has not performed Ruku, he should first stand up and then go into Ruku. If he does not stand up first, and performs Ruku while he is bowing, his prayers will be void because of not having performed qiyam (standing) before Ruku (Qiyam muttasi'l ba Ruku').