I recently acquired a map and route guide from 1968 (the year that the MTA was created). The guide includes estimated trip times for all of the lines, which I thought I might post here. I'll start with the IRT lines, which are all listed as the time to midtown, and in some cases with the time for the remainder of the route and some not. To be honest, I think these times are wild -- trains must have been flying! Note the inclusion of the Third Ave El too...
1 - 242 to Times Square: 35 min
242 to South Ferry: 50 min
2 - 241 to Times Square: 50 min
241 to New Lots: 1 hour 30 min
3 - 148 to Times Square: 20 min
148 to Flatbush Av: 50 min
4 - Woodlawn to Grand Central: 35 min
Woodlawn to Flatbush Ave: 1 hour 20 min
Woodlawn to Atlantic Ave: 55 min
5 - 241 to Times Square: 45 min
241 to Utica Av: 1 hour 20 min
6 - EXP Pelham Bay to Grand Central: 35 min
LOC Pelham Bay to Grand Central: 40 min
7 - EXP Main St to Times Square: 25 min
LOC Main St to Times Square: 30 min
8 - Gun Hill to 149 St: 20 min