Where the time actually goes
The six zones on the form come to 198 minutes running one after another. Only 138 of those minutes are water. The other 60 are the soak gaps on the two slope zones, which run 18 minutes each in two cycles with half an hour between them.
Thirty percent of the schedule is spent doing nothing at all, and that is what makes a schedule overrun a window that the run times alone said would be comfortable. Anybody adding up their zone times on the back of an envelope is adding 138 and getting a pleasant answer.
Fitting, and the headroom figure
Against a four hour window starting at 04:00, 198 minutes finishes at 07:18 with 42 minutes to spare, using 83 percent of the window. The line worth reading there is the headroom multiplier: the run times could grow to 1.30 times what they are now before the schedule reaches the end of the window, because the soak gaps are fixed and do not scale with the runs.
That figure is what tells you whether a system has any room in it for August. A system at 83 percent of its window in the shoulder season, with the seasonal dial well below 100, has very little. One that overruns already has none, and the page then works the scaling the other way and prints what each zone would have to be cut to.
The interleaving bound
A controller that can start one zone while another is soaking does better than running them in order. The page prints the lower bound for that: 138 minutes here, which is the total water time, because no soak gap on this schedule is longer than the water still waiting to be run. The 60 minutes of gaps could in principle all be filled.
It is deliberately a bound and not a schedule. Whether your controller does this at all is a feature question and many do not, the ones that do label it differently from one another, and a real interleaved schedule also has to respect that the soaks on one zone cannot be shortened just because another zone wants the slot. Take the number as the size of the prize rather than as an answer.
The window is not yours to set
The hours field on this form is the one input nobody should be optimising. What days you may water, at what hours, and whether any of it needs registering are decided by your water utility, move with drought conditions and the season, and carry penalties for being wrong. Ask them, put their answer in the field, and treat everything else on the page as the part you can change.
Questions people ask
Why does my irrigation schedule run past the window?
Usually soak gaps. Cycle-and-soak splits a zone into pieces with waiting time between them, and that waiting time is on the clock even though nothing is watering. On the defaults here, 60 of the 198 schedule minutes are soaks — 30 percent of the window spent doing nothing. Adding up run times alone understates the schedule by exactly that much.
What is a realistic watering window?
Whatever your water utility allows at your address, which is a rule rather than a design choice and changes with drought conditions and season. This page asks you for it and does arithmetic against it. It does not suggest one, and any figure you read anywhere else is somebody describing their own jurisdiction.
Can I run two zones at once to save time?
Only if the supply can carry both, which is a flow question rather than a scheduling one, and only if your controller supports it. What the page does show is the interleaving bound — the shortest a schedule could be if a controller ran one zone during another soak gap without ever running two valves together. That is 138 minutes on the defaults against 198 sequential.
If the schedule does not fit, what should I cut?
The page prints the scale factor that would make the run times fit with the soak gaps unchanged, and what each zone becomes at that factor. Whether taking that much depth off is acceptable is a soil and planting question this page cannot answer. The other levers are more watering days if your rules allow them, fewer cycles on the slope zones, or reducing the precipitation rate of a zone so it needs less soaking in the first place.
Should the soak gaps be shorter?
That is a soil question, not a scheduling one. The gap exists so ponded water can go in before more arrives, and its length comes from the intake rate of your soil against the rate the zone applies. Shortening it to fit a window means accepting runoff. The precipitation rate calculator works the cycle and soak split from an intake rate you measure or get locally.