You used the term "processes returns", which has created some confusion. It can take up to 21 days for the IRS to process an efiled return in normal situations. If any manual review is required, it can take much longer.
However, are you instead referring to the efile status? i.e., did you recently efile in the last 2-3 days, and when you log into your Online account and look at the Tax Home, does it say the efile is still "pending?" i.e., have you not yet heard if the efile has been accepted or rejected? Once the efile is in accepted status, then the IRS begins to process it. Normally one will hear within 48 hours if the efile was accepted/rejected but at times it takes longer.