Thorn in my tyre tyre this morning, removed it and tyre went down, took tyre off and noticed the sealant has dried up! Is there a life span on this stuff??

Caffe latex is useless. It dries out in a few days. I used it once and had the same problem as you. Stans every time for me

Not had problems with the NRG sealant from On-One/Planet X, and it’s only £10-15 per litre (depending on their current offer).
I opened up a tyre that had had it in for nearly 9 months, and still plenty of liquid inside.