What is maximum fuse in Minecraft?(TNT Fuse)

The maximum TNT fuse is the largest number that can be stored in a NBT TAG_Short, which is 32767 ticks. There are 20 ticks in a second, which means that 32767 ticks approximates to 00h:27m:18.35s.

Summoning a TNT with a maximum fuse is as simple as including the NBT for a /summon command:

/summon tnt ~ ~ ~ {Fuse:32767s}

The s is a data type, meaning that the number is a TAG_Short. It is a good practice to include your data types in the NBT, so that it's not ambiguous over which number type you want.