Timing Window

On Master, the timing window for a Perfect is 60ms and 80ms for a Great.
A Flick has a 150ms perfect window.

Yes so technically it's not too hard to hit a chord with one finger and still get perfect for both, but most of the time it's not easier.

Tap Area

You may tap anywhere from the very bottom of the screen to 80% of the height of the screen. The diagram below shows the registration area for each lane numbered 1 to 5. On aspect ratios wider than 4:3, the registration area for the lanes on both sides extend all the way to the extreme edge. An easy way to find out how high your device accepts tap inputs is to turn on tapsounds and tap around during the song title and READY animations. Keep moving your finger up until you stop hearing the sound effect for tapping, that's where the limit lies.

Flick Area

Unlike Taps, you may flick anywhere on the screen, but if you make too much vertical movement (flicking sharply upwards diagonally for example) it may not register. Make your movements precise and deliberate.

You may also cross your fingers when flicking, it registers both perfectly fine.

Hold Mechanics

A hold uses the same judgement window as a regular tap for both the start and the end of the hold. However, it is more lenient at the release due to technical quirks. You are frequently able to release very slightly early without dropping to a GREAT or NICE judgement.
Additionally, during a hold you are able to move your finger while holding. It can be anywhere on the screen, but cannot leave the screen. You can release the hold anywhere, you don't even have to return to it's origin for the release.

Flick Mechanics

Flicks require a direction movement to trigger the note registration. You do not need to tap to trigger a flick note; Your finger can be already on the screen.

The lines connecting flicks are just for show to make reading them clearer (but sometimes more confusing) You can release your finger at any time and it does not track which finger was used to start the sequence of flicks. You may flick each note one by one as a matter of fact, which will come handy on some slower patterns.

Flicks can be registered by a finger that is already holding down a hold note (Since you can move around the holding finger)

Slide and Checkpoint Mechanics

Slides function the same way as holds, except the release lane is judged as well. You cannot swap the holding finger while in a slide, nor can you lift the finger during the slide.

If the slide ends in a flick, you do not have to return to the correct lane to hit the flick, you can simply use your other hand.

Unlike holds, flicks cannot be hit by the sliding finger. Unless the flick is at the end of the slide.