The Past: We cannot change the past. In life it is sometimes useful to remember what happened though. Notably, when we are dead The Past will make up "who we were" so best not to ignore it entirely.
The Future: We can try our best to control the future by planning. With practice we can get good at planning, and we might achieve great things… alas, there is no 100% guarantee that these great things will happen. Nevertheless, planning is, by all accounts, prudent practice even without the guarantee.
Right Now: The reason why (of the three types of time) Right Now is the most important, is that we have 100% control over it. Not over what is taking place, but of how we view it… We can choose to make right now positive / happier / productive / restful
Meticulously planned or recklessly ignored, every second of The Future eventually becomes Right Now… and then, as each second passes through our consciousness, our brains have the final say on where those moments are filed in The Past.
Managing Right Now and processing those moments positively is the most important administrative role our brains have, because when the clock winds down, and The Past is all we have left, there's no going back to reorganize those files.