You need more than an hour to make the most of your time at Tanah Lot Temple.
It can be very crowded where the iconic island temple is because everyone who is there MUST have a photo taken with the temple as the backdrop. I was there at low tide & we could walk across the narrow channel to where the Island temple stands.
To get away from the madding crowd after taking some photos of the iconic temple, just walk westward to get a nice view of the sunset. The crowd thins out as you move westward and the ground there is worth exploring too. There are some lesser known shrines along the way where the locals pray and there are also some stalls, not shops selling souvenirs on the pavement. There are good photo opportunities (& fewer people) there besides the iconic Island temple. The additional bonus when you move westward is a better view of the sunset.