Update: It's worth noting that ballots accepted from 7 to 9 p.m. will be provisional ballots. A press release from Travis County Clerk Dana DeBeauvoir has more:
Pursuant to Texas election laws, ballots cast by individuals who arrive at a polling place after 7 p.m. but before the polls close, will be voted as provisional ballots. Ballots cast provisionally are reviewed by a ballot board and will be accepted as long as the voter is otherwise qualified. Votes casts by eligible voters during extended hours will be counted and included in the final tally, however, results from these ballots will not be included in this evening’s unofficial vote totals.
“We appreciate the dedication and stamina of our election workers who will be working long into the night.” said DeBeauvoir. “Elections wouldn’t be possible without the efforts of these steadfast and faithful citizens who conduct elections under extraordinary circumstances.” DeBeauvoir added.
Some observers are already discussing what effect those ballots could make – especially in one Travis County race. Jim Henson, director of UT-Austin's Texas Politics project, tweets "That ringing sound you hear? Calls from[Andy] Brown, [Sarah] Eckhardt to election lawyers."
Update (2:40 p.m.): A judge has granted a request to keep Travis County polling places open an extra two hours tonight - until 9 p.m. - after icy weather caused voting officials to delay opening polls until 11am this morning.