Personally, I haven't had much luck with Polymarine adhesives (caveat: I'm in the US, so shelf life may play an issue here.)
It's all in the preparation, ambient air temperature and how the repair is completed. Polymarine's 2-part PVC glue includes an adhesive and curing agent. I repaired the seams, end cones and transom on my Zodiac CGT (circa 1986).
Washed boat thoroughly and allowed to dry. Areas to be glued were sanded to remove any old glue and provide a key for the patch to adhere to. The underside of the patch was sanded too. Area to be patched was degreased with MEK twice and allowed to dry. Mixed up the 2-part glue in a jar working quickly (latex gloves a must). Applied a coat of adhesive with a brush to the boat fabric and to the patch. I allowed 15 minutes between coats. The second and final coat of adhesive was applied and then left for a further 15 minutes until it developed an oxidsed glaze. The patch was applied to the boat, working from the centre, applying pressure out to move any air bubbles to the edge of the patch. Excess glue was removed from the tube and the patch with solvent. A little chalk dust added and then a heavy weight applied on top of a flat surface (wooden shelf or bit of MDF) to ensure there was consistent pressure across the entire surface of the repair. Left to dry and cure for 36 hours in a garage. Temperature-wise it was probably in the 15-20 degree Celcius range. Worked for me.