Change: Use seconds for Linkgraph update settings (#10610)

src/saveload/afterload.cpp

@@ -799,6 +799,12 @@ bool AfterLoadGame()
 		_settings_game.game_creation.ending_year = DEF_END_YEAR;
 	}
 
+	/* Convert linkgraph update settings from days to seconds. */
+	if (IsSavegameVersionBefore(SLV_LINKGRAPH_SECONDS)) {
+		_settings_game.linkgraph.recalc_interval *= SECONDS_PER_DAY;
+		_settings_game.linkgraph.recalc_time     *= SECONDS_PER_DAY;
+	}
+
 	/* Load the sprites */
 	GfxLoadSprites();
 	LoadStringWidthTable();

src/saveload/saveload.h

@@ -350,6 +350,7 @@ enum SaveLoadVersion : uint16 {
 	SLV_VELOCITY_NAUTICAL,                  ///< 305  PR#10594 Separation of land and nautical velocity (knots!)
 	SLV_CONSISTENT_PARTIAL_Z,               ///< 306  PR#10570 Conversion from an inconsistent partial Z calculation for slopes, to one that is (more) consistent.
 	SLV_MORE_CARGO_AGE,                     ///< 307  PR#10596 Track cargo age for a longer period.
+	SLV_LINKGRAPH_SECONDS,                  ///< 308  PR#10610 Store linkgraph update intervals in seconds instead of days.
 
 	SL_MAX_VERSION,                         ///< Highest possible saveload version
 };