When will I receive the BFS letter confirming the amount of my refund offset?

Neither the IRS nor the BFS website suggests a timeframe in which you can expect to receive a letter. 

However, https://www.irs.gov/taxtopics/tc203 has a contact phone number to call for more information.   (I’m not listing the number here, since this post might be accessed in the future, and the phone number may change.)

When l checked my refund status the IRS said l was approved for direct deposit however my refund may be reduced partially it completely due to something I may owe. If so l would be contacted be the BFS. My question is, does this mean l owe or is it something everyone has stated on the website when the see and approved direct deposit bar?