millis()
Returns the number of milliseconds since a sketch started running.
millis() keeps track of how long a sketch has been running in milliseconds (thousandths of a second). This information is often helpful for timing events and animations.
Examples

function setup()
size(100, 100)
background(200)
fill(0)
-- Get the number of milliseconds the sketch has run.
local ms = millis()
-- Style the text.
textAlign(LEFT, CENTER)
textSize(10)
-- Display how long it took setup() to be called.
text('Startup time: '..round(ms, 2)..'ms', 5, 50, 90)
describe(
'The text "Startup time: '..round(ms, 2)..'ms" written in black on a gray background.'
)
end

function setup()
size(100, 100)
describe('The text "Running time: S sec" written in black on a gray background. The number S increases as the sketch runs.')
end
function draw()
background(200)
fill(0)
-- Get the number of seconds the sketch has run.
local s = millis() / 1000
-- Style the text.
textAlign(LEFT, CENTER)
textSize(10)
-- Display how long the sketch has run.
text('Running time: \n'..str(round(s,1))..' sec', 5, 50, 90)
end

function setup()
size(100, 100)
describe('A white circle oscillates left and right on a gray background.')
end
function draw()
background(200)
-- Get the number of seconds the sketch has run.
local s = millis() / 1000
-- Calculate an x-coordinate.
local x = 30 * sin(s) + 50
-- Draw the circle.
circle(x, 50, 30)
end
Returns
Number: number of milliseconds since starting the sketch.