I applied the day separators manually, just as you did.
The double vertical lines on my chart denote [I]early[/I] Sunday trading (2pm-5pm, New York time), prior to the 5pm opening of the Monday trading day. In this particular platform (FXCM MarketScope), the trading activity represented by those early Sunday candles gets swept into the Monday Daily candle. So, on a Daily chart, there are simply 5 candles per week representing Monday through Friday, without a Sunday candle.
You are right. High tick-volume can (and often does) occur while price is seemingly constrained in a tight range. Each tick on a tick-volume chart represents a transaction which moved the price by one pip, or more. But, it’s entirely possible for successive ticks to represent aimless (trend-less) meandering of price within a range.
In similar fashion, price can (and sometimes does) [I]begin[/I] a large, directional move on very low volume. But, for that move to be [I]sustained[/I], significant volume will have to come into the market.
If you examine the times of day when prices [I]typically[/I] make significant, directional moves, you will find that those times [I]usually[/I] fall within the periods we have identified as periods of high volume.
So, if we know when daily surges in tick-volume [I]typically[/I] occur, we have a clue to [I]potentially[/I] profitable times to look for trades.
Note the qualifiers: [I]typically, usually,[/I] and [I]potentially.[/I] Trading is a game of probabilities, not certainties.
[I]Always[/I] and [I]never[/I] are words that [I]don’t[/I] describe price behavior.