This is just a dump of some ideas and stats that you should not take for granted, the data its most of the time inaccurate , because i run 2 commands at the same time.

But anyhow, its a point of conversation First, i had filtered with osmconvert and osmfilter so i remained with a planet dump, composed of only the tag highway I am trying to import all the roads in the world, after i tried with a direct attempt and did not scale up, i had now spitted the world into each continent

Size = only the highway , saved as a osm.pbf

africa_highway ( 356 MB ) = 46 Minute to import into postgis Asia_highway ( 1318 MB ) = 213 Minute to import into postgis Australia_highway ( 259 MB ) = 14 Minute to import into postgis Central America ( 63 MB ) = 10 Minute to import into postgis