Many couples planning to marry in the ACT have been hastily confirming their wedding plans after the High Court reserved until December 12 its decision on the Commonwealth's legal challenge to the territory's same-sex marriage laws.

Canberra couple Darlene Cox and Liz Holcombe will be the first same-sex couple to marry at the Margaret Whitlam Pavilion at the National Arboretum on Saturday.

The venue had given them a range of dates to consider, given the uncertainty over the court challenge.

''The Arboretum has been fantastic … because we didn't know when the law would be passed,'' Ms Cox said. ''So they've been wonderfully flexible and really supportive.''

The judgment gave couples a five-day window in which to get married, with the earliest weddings happening in the first minutes of Saturday morning.

Ms Cox said she had been incredibly touched by the flood of support from her fellow Canberrans.

''Whether it's a bit of local catering at the IGA or some flowers delivered, once I tell them what it's for there's been a sense of overwhelming support and goodwill,'' she said.

''I love being a Canberran and I love the fact that our Canberra is proud of the fact we can get married this weekend.''

Australian Marriage Equality deputy director Ivan Hinton had planned for a month to marry his partner of 11 years, Chris Teoh, this Saturday in Canberra. But their entire reception only came together in the past 24 hours.

''All I had as of yesterday afternoon was a celebrant, a patch of grass which we got from a lesbian couple and a jazz band,'' he said.

With the help of the Canberra Convention Bureau and some local hospitality providers, they will now have a private reception at Telstra Tower, whose lights will shine in the colours of the rainbow in the early hours of Saturday.

Convention Bureau CEO Robyn Hendry said she was happy to help.

''It's important to the ACT,'' she said. ''We think this is a moment in time. We have some skills and we've been working with Ivan in any case so we're very happy to assist.''

Mr Hinton said his wedding was open because he felt the day was about more than just him.

''It's not just about Chris and I,'' he said. ''This about Canberra, this about the people I live amongst and this is something we can celebrate.''