Whenever USCIS requires more information or detail on a case, they will issue a Request for Evidence (RFE). The RFE will have a deadline (usually 30 to 90 days from the date the RFE was issued) and the response must contain enough evidence to generate a favorable decision.
When USCIS issues an RFE, they stop processing the case, so the sooner you submit your response, the less your case will be delayed. Generally, USCIS will only issue one RFE. If your response is insufficient, your case will be denied and you may be placed in removal proceedings.