ClientTickEvent is the wrong event, you have to use ServerTickEvent. Also note that tick events fire twice every tick, check TickEvent#phase.
You cannot store variables like "tcount" in your item class, as there is only ever one instance of your item class so this variable will be shared between all instances of your item (e.g. if two players use it at the same time). You need to use either the ItemStack, a player capability or something like a global task system: A list of Runnables that your tick event runsy and which keep track of the timer themselves.