We encounter the world through the senses, as interpreted by the brain. That means our perception of events is delayed. So we can’t actually experience “now”. . .
I need a neural upgrade – my senses are too slow.
There’s a problem that brings furrows to my brow:
Whenever something happens, it’s a while before I know;
So, although it happened “then”, to me it’s “now”.
We’re all living in the past because the present’s been and gone
By the time our senses recognise it.
Our poor brains, the last to know it, do their best to work upon
All the data coming in, to analyse it.
Then our brains make moving “pictures”, but the fact we can’t ignore
Is: however good the “movie”, or how pleasant,
Like film the pictures only tell of what has gone before –
So it’s true to say there’s no time like the present.
See also What time is it? and Now and then.