How long is the delay to update distance walked?

Anytime the "loading" symbol appears in the corner, your distance is usually not being counted. If you wait for the game to finish loading before you walk, your distance will almost always count. The update is dependent on whether it is able to get a good GPS signal but even if you have excellent signal, if the game is loading it will not update until it has finished loading. At least, according to a number of experiments done by a few people that seem to show that distance is not counted while the game is loading. This would explain the jumps you experience as well, I would think. Hope this helps.

Well the delay will depend on your connection of course, if you have a poor connection it will probably be longer than if you have a good one.

But there is no fixed amount of time between each delay to update the distance to hatch the egg, it's purely based on connection.

Hope this answers your question.

the interval time between updates on egg hatching and buddy system is 5 minutes. every 5 mins to the second the buddy system will add on the last clocked distance. I am still figuring out exactly how long between each location check that adds the distance but for it adding to your buddy/egg it is 5 minutes. if you get a loading circle at the 5 minute mark it will delay the add up until the loading is done, giving the impression the next one is shorter but it still keeps to the 5 min mark. the counter starts the moment the game has finished loading. If the game loads, and the character is displayed at XX:37, this counts as the first location marker, 5 minutes from then, XX:42 it will add the next totalled distance to the buddy, and XX:47; XX:52 and so on

don't forget the most effective way to clock distance is to walk in a straight line. the game checks your location at certain intervals, draws a straight line between them and uses that as a distance (if you travel to fast between two points it thinks your driving - so no switching between apps or staying too long in the caught pokemon screen). i.e. walking in a straight line for 1 km will clock 1km in distance; walking in a 1km circle will only clock about 600m as it only clocks a triangle between 3 points rather than your actual path taken.

I usually walk 1km in a straight line, wait for the distance to be clocked in the buddy and turn around 180degrees and walk back 1km. doing this and checking my distance I have clocked 2km. if you do need to make a 90degree turn or more I would advise waiting for the buddy to clock the distance before carring on as you would have walked more than what has been clocked.

Your registered or virtual distance will update at a minimum interval of four (4) minutes. The interval could be longer than four minutes due to how iOS/Android keep track of time but is guaranteed to be no sooner than four minutes.

You may verify this by walking until your buddy Pokemon finds at least two candies (using 1 km buddy would be fastest). Then check your journal for the times when your buddy found the candies. Repeat this experiment several times to narrow down the update interval.