The U.S. Department of State (DOS) issues a certain amount of immigrant visas and green cards each year. Due to a large number of applications, some of the family-based and employment based petitions have to wait in line for their turn due to the limited quota. DOS allocates the spot based on country of origin and petition type, in order to maintain an appropriate diversity ratio. The Visa Bulletin is the monthly publication which updates the current waiting times of different visas for applicants from different countries.
Most of RapidVisa customers do not fall into any such quotas. However, if you are a green card holder petitioning for a spouse or unmarried children or if you are a U.S. citizen petitioning for an overage or married children or siblings, you need to check the visa availability at the most recent visa bulletin. To see the most recent visa bulletin, see the official site here.
If you are an applicant from China (mainland born), India, Mexico or Philippines, you'll need to check the time in the specific country column. All other countries can check the second column which said 'All Chargeability Areas Except Those Listed'.