Your average low night temperatures are similar to mine and we both live in Mediterranean climates, so I would suggest not planting it out until later. Winter is just risky for seedlings especially ones that have not been hardened off to the outside climate. I would suggest repotting it now and giving it as much warmth and sunlight as possible. Near the end of winter, on warm days, let the seedling stay outside if temperatures are above 15-18 degrees Celsius, but still take it in at night. Make sure to give the seedling part shade when growing it outdoors. I would suggest keeping it in a pot for at least another year before planning it outdoors. In our climates, summers can be hot and dry, and seedlings really don't like that combination. You can grow the jackfruit outside in a pot spring-fall as long as you keep it well watered and in part shade.
I won't even plant a jackfruit in the ground until it has been growing outside in a 5 gallon pot for over a year and is around a 0.75 to 1.0 meter tall. I am probably being overly cautious, but I have killed several small seedlings that were not ready to be grown outside, and learned the hard way to take it slow and let them adjust to the outdoor climate.