But she told reporters that she "doesn't five a f*** what her time is" because all she wanted to do was to raise money to help the NSPCC.
Natalie Dormer, who was running to raise money for ChildLine, said: "I'm here today because 3,000 children get in contact with ChildLine every day. And we don't have enough money to talk to every single one of them."
She is among 900 others running for NSPCC to raise money for the charity to ensure more children can be heard.
The actress said she had personally raised over £5,000 for the children's charity.
In total, today's NSPCC runners are hoping to raise over £2.3 million.
Running the course in three hours and 51 minutes, the actress said she was happy to see her time was at least consistent.