The line format
Each line is a start time, an end time, and then whatever the block is. 9:00 AM - 10:30 AM Design review #work is the full shape. The separator between the two times can be a hyphen, an en or em dash, a tilde or the word "to". Anything after the times is the label, and any #tag inside it is pulled out for the tag totals and removed from the label text.
Times without AM or PM are read on a 24-hour clock, so 14:00-15:30 is the afternoon and 2:00-3:30 is the small hours of the morning. If exactly one of the two times carries a meridiem, the other inherits it — 1:00-2:30 PM reads as the afternoon, which is what almost everyone means when they write it that way. Mixing an explicit AM start with an explicit PM end works as written.
A block that crosses midnight has to be split into two lines, one ending at 24:00 and one starting at 00:00 on the following day's plan. The tool models one calendar day and refuses a block whose end is earlier than its start rather than guessing which of the two you meant.
Collisions and the two different totals
Every pair of blocks that share even a minute is reported, with the exact overlap. This matters more than it sounds, because two half-hour collisions in a morning look like nothing on a list and mean you have promised to be in two places for an hour.
Two totals are shown and they are not the same number. "Blocks added up" is the plain sum of every block's length, so a half hour that two meetings both claim is counted twice. "Actually occupied" merges the overlaps first, so it is the amount of the day that is genuinely spoken for. When those two figures diverge, the size of the gap between them is the size of your double-booking problem.
Unbooked time is measured inside the window at the top, not across the whole 24 hours. Set the window to your actual working day and the unbooked figure means something; leave it at midnight to midnight and it will tell you, accurately and uselessly, that you are asleep for a large part of it.
What the tool leaves out
There is no travel time between blocks. If two blocks are back to back in different buildings, the timeline shows them as contiguous because that is what you typed. The honest way to model the journey is a block of its own, which is why the sample data has commutes in it.
There is no time zone handling anywhere in this page. Every value is a wall-clock reading in whatever place you happen to be. A call at 4 PM Eastern is only correct on this timeline if you convert it to your own local time first and enter that.
Nothing is uploaded and nothing is stored. The page holds the day only while it is open. If the plan is worth keeping, print it or copy the text out — that is the whole of the persistence story, deliberately.
Questions people ask
Can I enter a duration instead of an end time?
No, and the reason is the timeline. A duration without a start has no position, and a start with a duration is just an end time you have made the tool compute — the same keystrokes with an extra step. If you have a list of tasks with durations but no times yet, look at the open stretches table first, decide which stretch each task goes in, then write the lines.
Why is a block drawn narrow?
Because it collides with something. Blocks are packed into lanes, and the number of lanes is the maximum number of blocks running at once, so three simultaneous blocks each get a third of the width. Narrow bars are the visual signal for a conflict, matched by an entry in the collisions table. Remove the conflict and the bar goes full width.
How is time split when a block carries several tags?
Evenly. A two-hour block tagged #work and #travel puts an hour against each. This keeps the tag column adding up to the same figure as the blocks total, which would not be true if both tags claimed the full two hours. If a block is genuinely 90 percent one thing, split it into two lines with the real times rather than relying on tags to express the proportion.
Does it account for time zones?
It does not, in any way. There is no zone setting, no conversion and no daylight-saving adjustment. Times are wall-clock readings and stay exactly as typed. If your day involves other zones, convert to your own local time before entering, and treat a day containing a clock change as two separate plans.