Keeping a lookout whilst doing a visual approach isn't in your SOPs either I bet, it's airmanship, something you're taught during training. I tend to start the chrono so that IF we have an engine failure, or windshear or any other situation that requires TOGA during the T/O run or soon after, I know roughly how long I have been using it for, without having to worry about taking my hands off the thrust levers once I have selected TOGA. I tend to start the ND chrono and the internal clock chrono, but cancel the ND chrono at thrust reduction altitude. I leave the internal clock running in case of ACARS failure to be able to record T/O and Landing times.
Max time at TOGA with both engines operating is 5 minutes, single engine 10 minutes. However, there's a reason there's a limit and if you only have one engine running anyway, you may want to think about reducing thrust back to max continuous asap.