There are several crude approximations for estimating time when walking non flat terrain.

E.g. for this walk from the train station to the hospital - https://valhalla.openstreetmap.de/directions?profile=pedestrian&wps=11.249715685844423%2C47.28104865174184%2C11.24449610710144%2C47.2835305523123 Valhalla estimates 9min20sec. Very sportive :) Walking speed set to 4km/h estimates 12 minutes, still not bad for this journey :) For the record:

On https://en.wikipedia.org/wiki/Naismith%27s_rule Under Langmuir corrections it says: 4 km/h distance + 450 m/h of ascent, that makes

600 m => 1/40*6 => 0.15h
+ 1/450*90      => 0,2h
                   ----
                   0,35h => 21min

On https://www.alpenverein.at/portal/news/aktuelle_news_kurz/2018/2018_06_14_wie-berechnet-man-die-gehzeit-auf-wanderwegen.php it says: 300m/h ascent, 500m/h descent, 4km/h distance and a formula: The smaller value gets halved and added to the larger one:

90m elevation => 90/300   => 0.3h
600m distance => 1/400*60 => 0.15h
                             ----
0.3+0.15/2                => 0.375 => 22.5min

Estimates on guideposts usually have a granularity of quarters of an hour, so a guidepost there would read half an hour. This issue not a bug report, just an idea for enhancement. Though, if you care for hiking, this should get in, because wrong estimates on duration are in the top reasons for people calling emergency.