Laptop Input Lag

On my Brother's HP Notebook 14-dq1010nr, there is no input lag for 15 seconds or so of launching the world, but then it starts. When I press the move keys down I get no output for about 0.3 seconds and then it outputs. Same thing on the other side, 0.3 seconds for it to stop registering you are pressing keys. BTW, this ONLY HAPPENS in Minecraft. And I don't know why.