"polling day" refers to the day when people go to vote in an election. It's the designated day for citizens to cast their votes and choose their preferred candidates or express their opinions on certain issues. Full definition
The party has managed to bounce back before polling day in the past. (independent.co.uk)
Even on polling day there were people who thought you really wanted us to leave. (mirror.co.uk)
The investigation into the causes of the party's electoral collapse reveals that senior figures were hoping to win 23 to 30 seats right up until polling day. (theguardian.com)