SAN FRANCISCO – Dozens of gay couples planned to rush down to their county clerk’s office Monday evening to be among the very first to say “I do” under the historic court ruling making California the second state to allow same-sex marriages.

The May 15 decision by the California Supreme Court was set to take effect at 5 p.m. While Mondays are not exactly a big day for weddings, at least five county clerks around the state agreed to extend their hours to issue marriage licenses, and many gay couples planned to get married on the spot.

“These are not folks who just met each other last week and said, ‘Let’s get married.’ These are folks who have been together in some cases for decades,” said Kate Kendell, executive director of the National Center for Lesbian Rights. “They are married in their hearts and minds, but they have never been able to have that experience of community and common humanity.”

The really big rush to the altar in the nation’s most populous state is not expected to take place until Tuesday, which is when most counties plan to start issuing marriage licenses to gay couples. Hundreds, perhaps thousands, of couples from around the country are expected to seize the opportunity to make their unions official in the eyes of the law.

Local officials will be required to issue licenses that have the words “Party A” and “Party B” where “bride” and “groom” used to be.

A conservative Christian legal group asked a state appeals court to block the weddings, but the move was given little chance of success. California’s high court rejected a previous request for a postponement.

As of Friday, nearly 620 couples had booked appointments to obtain licenses at San Francisco City Hall over the next 10 days.

Clerks elsewhere around the state reported nowhere near as high a demand but said they were training volunteer marriage commissioners to officiate at civil ceremonies in anticipation of a surge in business.

Unlike Massachusetts, which legalized gay marriage in 2004, California has no residency requirement for marriage licenses, and that is expected to draw a great number of out-of-state couples. The turnout could also be boosted by New York state’s recent announcement that it will recognize gay marriages performed in other jurisdictions.

However, Some couples may wait to tie the knot because of a proposed constitutional amendment on the California ballot in November that would undo the Supreme Court ruling and ban gay marriage.