Timlin broke his leg during the Johnstone's Paint Trophy Southern Area final first-leg victory against Leyton Orient in the first and Mayor was brought in just hours before Tuesday's clash with Cheltenham.
The 22-year-old joined from Sheffield Wednesday on an initial 28-day loan deal and slotted straight into the Shrimpers' starting line-up.
And Sturrock believes Mayor will boost the club's promotion hopes and is pleased that he will be available for the second leg against Orient as Southend aim to get to Wembley.
He told the club's official website: "With the news that Michael Timlin would be out for the rest of the season we looked to bring someone in.
"Danny is a quick wide man who will cause problems for defenders. We're delighted to have been able to bring him in.
"With Michael out injured and Marc Laird and Michael Spillane cup-tied, it's a bonus that Danny will be available for the Johnstone's Paint Trophy."