Trainers and owners will have six weeks longer to decide on Investec Oaks entries this year, with the fillies' Classic closing at noon on Tuesday, 14th April, rather than in early March.
The Investec Coronation Cup for older horses will also close on the same day, which is a week later than in previous years.
Explaining the changes, Andrew Cooper, Head of Racing at Epsom Downs, said: "We have felt for some time that the first week of March is early enough in this day and age for us to be seeking entries for a race of this nature in three months' time - particularly given how fillies can be slow to come to hand in the spring.
"The extra time now available to connections before the entry deadline will mean they are better placed to judge their filly's potential for the Investec Oaks.
"The March closing date was purely historic, and we think it may have been costing us entries in recent years, particularly from overseas. To keep things simple for everyone, it makes sense to close the Investec Coronation Cup on the same day."
The Investec Oaks, for three-year-old fillies, is one of the two British Classics staged at Epsom Downs Racecourse during the Investec Derby Festival, being run on the first day, Investec Ladies' Day, Friday, June 5.
Newmarket handler Ed Dunlop has won the Investec Oaks twice with outstanding fillies - Ouija Board in 2004 and Snow Fairy in 2010 - who both went on to record multiple top-level victories around the world.
The trainer welcomed the entry date change for the Investec Oaks: "I think this is good news and it may make trainers enter fillies which have been slower to come to hand.
"As a trainer, in an ideal world, I would love the race to close even later but that is not possible.
"It doesn't make a great deal of difference in terms of the trials, as the closing date is still before the trials start taking place.
"However, the change of date could certainly help in attracting more entries from overseas, for example from France where the trials' season gets going much earlier in the year.
"The only fillies you would lose from the entries are those who were being aimed at the race and have a setback between March and April, or are disappointing in their work."
The 2015 Investec Oaks is boosted in value to £450,000, up from £425,000 last year. As a result, and in line with BHA guidelines, the cost of entry for the Investec Oaks rises to £1,500 from £1,325.
The Investec Coronation Cup and Investec Derby, Britain's premier Classic, happen on Saturday, June 6. Initial entries for the 2015 Investec Derby were made in December, 2013, at the yearling stage. There is a scratchings' stage for the Investec Derby on March 3, with an £8,000 second entry opportunity on April 7. The 2015 Investec Derby has a prize fund of £1.325 million, making it the richest race run in Britain.