Most vases of flowers last around 4-7 days, depending on the flowers and the care taken.
To keep your arrangement longer, a preservative helps a lot to lengthen the arrangement. To survive cut flowers need three things: Carbohydrates for cell metabolism; biocides to prevent bacterial growth and to help keep the flowers healthy; acidifiers to lower the pH value so the flowers absorb more water and therefore are more nourished.
One useful suggestion is to put an aspirin in the floral arrangement to help the flowers last longer. But the effectiveness is probably the effect of the carbohydrates the aspirin contains. Another suggestion is to put a penny in the vase with the flowers. The copper in the penny is supposed to lower the pH value which makes the flowers absorb more water. But pure copper pennies are unfortunately not minted anymore.
Cut flowers like being in a cool spot out of direct sunlight. Keep them away from vents or radiators which could give of shafts of warm air.
