YAY! Wedding Favours would say that your bomboniere can be ordered anytime from 1 month to 3 months in advance.
It all depends on which bomboniere you are choosing and if the gift is custom made or off-the-shelf.
Even if it is off-the-shelf, it still needs time for the branding and also to secure the blank stock.
Sometimes it is tough to order so far in advance.
I always suggest to over order the quantity of bomboniere over and above the expected guest count. With the extras, you can gift as a thank you to your; celebrant, photographer, car driver, flower arranger, reception venue host, hairdresser, make-up artist etc who are apart of your special day, but don't get to be at the reception.
If the gifts are personalised with guest names, that makes it a bit harder for timing while you await the RSVP's. But even still, ideally allow 4-8 weeks in advance. That way you can cross it off your 'to-do' list as early as possible.