306.03 Effect of Filing by Fax
The filing date of correspondence received in the USPTO by fax, regardless of whether it contains a certificate of transmission, is the date that the complete transmission is received by a USPTO fax machine, unless the transmission is completed on a Saturday, Sunday, or Federal holiday within the District of Columbia. Correspondence for which transmission is completed on a Saturday, Sunday, or Federal holiday within the District of Columbia is given a filing date as of the next succeeding day that is not a Saturday, Sunday, or Federal holiday within the District of Columbia. 37 C.F.R. §2.195(a)(3).
For example, a 20-minute fax transmission to the USPTO from California starting on a Friday at 8:45 p.m. Pacific Time would be completed at 9:05 p.m. Pacific Time. The complete transmission would be received in the USPTO at approximately 12:05 a.m. Eastern Time on Saturday. The filing date accorded to the correspondence is the date of the following business day, which in this case would be Monday (assuming that Monday is not a Federal holiday within the District of Columbia).
The phrase "complete transmission" means that the transmission was received in its entirety. For example, if page one of a ten-page fax transmission is received in the USPTO at 11:55 p.m. on a Tuesday and page ten of that transmission is received at 12:05 a.m. Wednesday, the filing date accorded to that correspondence will be the date of that Wednesday (assuming that Wednesday is not a Federal holiday within the District of Columbia).
If the sender wants the correspondence to be considered timely filed as of the date that the transmission began, the correspondence must include a certificate of transmission under 37 C.F.R. §2.197(a). See TMEP §306.05(c) regarding the effect of a certificate of transmission.