Graduation in Paris: French peonies in bac week, and what follows
For graduation in Paris, the written baccalauréat papers come in mid-June, on dates set each year, with the philosophy paper among them. French growers are still cutting peonies through that same week, since their season runs from late April to June, so the choice comes down to a bunch of real peonies while they last, or flowers built to outlast a week of exams.
French peonies in bac week, and roses cut to their shape
French growers are still cutting peonies in mid-June, at the tail of a season that runs from late April. Between February and April the gap is filled by growers in Israel, Italy and France.
Peony-shaped roses such as 15 Peony Lavender Roses fill the same silhouette without needing the season at all. Most are English David Austin varieties, carrying the same layered, cupped head as a peony but cut to a rose's own calendar.
A peony bought at the marshmallow stage, when the coloured bud gives slightly under a finger, opens over a day or two in warm water and good light. Once fully open, it holds five to seven days in the vase. Peonies are worth choosing now, while the French season still runs.

A rose lasts about a week in a vase, sometimes up to ten days. Roses are worth choosing at that stage if they need to survive more than one evening. Carnations and chrysanthemums go further still, both lasting two to three weeks; chrysanthemum, though, is France's flower for Toussaint, not a gift for a June visit. The carnation end of that list is sold as carnations (15 Dianthus).
Lily pollen stains fabric once the flower opens, so the anthers are pinched out as soon as it is fully out. The same flower is worth ruling out for any home with a cat, since lilies are toxic to cats.
A bouquet wrapped in plain kraft paper is the easiest of the formats to carry across a metro platform or up a staircase with no free hand for a vase. That holds true after the last written paper, nothing more: the wrap makes the flowers easier to hold, not longer-lasting.

Graduation flower delivery in Paris to the family flat
A box or a basket stands without a vase, stems already resting in soaked foam, which suits a family flat better than a hand-tied bunch needing one found and filled. The catalogue's 25 Mixed Roses in a Box is one way into that format, and a floral handbag does the same job for a bouquet meant to be carried rather than set down.
One flower is worth leaving out of a bouquet for a French family: chrysanthemum is France's flower for Toussaint, with 64% of chrysanthemum sales falling around the first of November, so it is not given as a present.
Every bouquet is put together once the order is placed, not pulled ready-made off a shelf, and the finished arrangement is photographed before the courier leaves. A card goes in free, and balloons or sweets can be added to a basket; most orders reach the family the same day they're placed, with the exact window for a given bouquet shown on its own page. Paris is priced by zone, with the centre delivered free, and the zone and price for any address appear on the delivery page before payment. Ordering from another country, sending to a hotel or giving only the recipient's phone number all work the same way, and that side of it is covered on the flowers section.
A basket is the easier starting point for a family flat, flowers in boxes work the same way for a desk or a hallway table, and gifts to go with the bouquet cover the rest of the evening.