Marking a half-year milestone? 26 weeks from today is exactly 182 days out, since 26 × 7 = 182. That's the closest a whole number of weeks ever gets to splitting a 365-day year cleanly down the middle. That is why 26 weeks is the number people reach for when they say "half a year."
What time was it 7 hours ago? Take seven off the current hour and keep the minutes exactly as they are. If it is 5:25 PM right now, seven hours earlier was 10:25 AM the same day.
Trying to work out how long until 2:45 PM it is right now? Count forward from the clock to the next 2:45 PM — today if it has not arrived yet, or tomorrow if it has already gone by. At 1:15 PM that gap is 1 hour and 30 minutes. At 2:29 PM it has shrunk to just 16 minutes.
Setting a target roughly half a year out? 24 weeks from today lands exactly 168 days ahead, no matter which month you start counting from. The trick is one multiplication: 24 × 7 = 168. Add that many days to today's date and you have your answer.
Need to know how long until 2:40 PM? Check your clock. Then count forward to the next 2:40 PM — today if it hasn't arrived yet, or tomorrow if it already has. At 11:50 AM, that gap is 2 hours and 50 minutes. At 2:25 PM, it shrinks to just 15 minutes.
What time will it be 7 hours from now? Take your current clock time, move the hour hand forward by seven, and leave the minutes exactly where they were. Starting from 8:35 AM, you land on 3:35 PM that same afternoon.
What time was it 4 hours ago? Take four away from the current hour and leave the minutes untouched. If it is 1:50 PM right now, four hours earlier was 9:50 AM the same day. That is the whole idea in one sentence.
Trying to work out how long until 2:30 PM? Check the clock. Then count forward to the next 2:30 PM. That means today, if it has not passed yet. It means tomorrow, if it already has. At 11:50 AM, the gap is 2 hours and 40 minutes. At 2:05 PM, it shrinks to just 25 minutes.
Mapping a semester, a training cycle or a long project runway? What date is 16 weeks from today comes down to one move. Add 112 days to today's date. Sixteen weeks lines up neatly with a college semester and many structured programs. That is why it shows up on so many calendars.
How long is it until 2:25 PM? Look at the clock, then count forward to the next 2:25 PM — today if it hasn't happened yet, tomorrow if it has already gone. At 9:40 AM, that gap is 4 hours, 45 minutes. At 2:19 PM, it shrinks to just 6 minutes.