The latest revision in the git repository seems to use the sets->get_use_timeline() function as a two-bit field instead of a binary flag. See gui/welt.cc around line 494 and the comments suggest LSB as "timeline on" while second bit (value 2) for "pakfile permits user to enable/disable timeline" -- for example,
gui/welt.cc:493: if(sets->get_use_timeline()&2) {
However, many places in the code still expect this to be a simple boolean flag, as for example:
player/ai_passenger.cc:1466 if(welt->use_timeline() && line->count_convoys()>1)
...
gui/citybuilding_edit.cc:118: if(!use_timeline || (!besch->is_future(month_now) && (!besch->is_retired(month_now) || allow_obsolete)) ) {
{
The net result is that even when the timeline is turned on in the New Game dialog, new cities are built as if the timeline were off. I tested this with the latest Pak128.Britain-Ex from the git repository, whose new simuconf.tab has use_timeline = 2.
Stylistically, use of magic numbers like 1 and 2 in code should be avoided; a constant should be defined... and the remainder of code using what was formerly a simple flag must be checked to verify it is handled as a bit-field.
Bottom line, the timeline option is currently broken. Changing simutab.conf to have use_timeline = 1 at least makes things work.
Thank you for the report - I have now reverted my changes here back to the code as it is in previous versions and Standard. I have found that the proper way of having the timeline set on by default but able to be turned off in the new world dialogue is to have use_timeline = 3 in the pakset's simuconf.tab: having it in the base simuconf.tab will not suffice, it seems.