At most 1 year.
He could probably only last for another year if Fei Yang Kingdom didn't manage to conquer Zhang Xu Kingdom and send him reinforcement. After all, the battle would naturally cause his soldiers to die because of the battle.
Once the number of soldiers were insufficient to face the soldiers from Shi Long Kingdom, it would mean trouble.
'Brat, how long are you going to postpone. It's already spring.'
Great General Long snorted and waved his hand. His son was still as annoying as ever and didn't even want to leak out his plan to his own father. He had to use his own brain to think about what his son might be planning.
"Raise the line. We're going to attack!"
"Yes!"
…
<North border of three kingdoms, Fei Yang Kingdom, Fan Yi and Zhang Xu Yu Jin's Location>
Clang! Clang! Clang!