Just would like to share my experiences, eg timeline and provided materials, as a guide for whoever thinking of applying Tier 1.
Submitted my application on the 28th May, Wednesday
Receive the acknowledge of receipt from home office on 4th June, Wednesday
Didn’t hear anything until receive the approved application on 15th July

Provided materials:

Passports
Coverletter for my application, list of all awarded points and paid
Statement of attendance from my university in UK
Original certifiicate from my university
Statement of employment from my current employer(was working under IGS earlier)
11 pieces of payslips instead of 12 as before that I was student
11 pieces of bank statement which show the amount of the payslips in my account

I am so relieved now. Although the application form is >40 pages, and it is not easy to get approved, I think it is certainly do-able without the help of consultancy, which charge at least 1000pounds. Anyway, good luck!!