I agree with Mark, you'll probably want to get a cask now and fill it with something else yourself, even if it's just warm water. When you put the mead in, taste it every couple of days or even daily - a cask with that high of a surface/volume ratio can quickly get over oaked. When it gets to where you like it, take the mead out and then refill the cask with the mead as close to the event as possible. I'd actually be tempted to oak it with cubes, then put it in the cask the night before the wedding.
If you're talking about giving it to them to drink themselves over the course of the month, I wouldn't put it in until the wedding anyway, it will pick up a lot of flavor over the month. Or put it in the barrel for a while and then bottle it so they can drink some that month and save some for future anniversaries.