The 'one' has far bigger issues heading out of the city in the evening peak, Dumbarton Road has an increasing number of points where congestion causes considerable delays to services. Recently when I have been heading west from Scotstoun between 4.30 and 5.30 the buses on the 'one' corridor are normally 10 to 15 minutes late. Getting through Dalmuir is another example where around 5pm services have no chance of maintaining the timetable. Once the hospital and the industrial estate have cleared it does ease off quite quickly but by that time the damage has been done. Unfortunately, however I don't see how it can be fixed without investment in significant priority infrastructure improvements, to manage the timetable would require extra buses being fed in on the other side of the congestion.
This is the main problem. You can put in additional time into the schedules but without bus priority and enforcement, you're subject to the whims of the traffic on any one day. Bus companies DO try to make schedules achievable but it's a balance and you can never second guess when some courier van sits in a bus stop, hazards on, whilst delivering someone's Amazon parcel, or a set of temporary traffic lights appears like Brigadoon.
To choose another example (picked at random), look at the 60/60A. From Killermont Bridge to Renfrew St, it takes 17 mins first thing in the morning when the roads are clear. By 0630, it's 22 mins, and by 0730, it's got 27 mins - they've added 10 mins to cope with peak hour traffic. As per the 1, the evening service has less extra time added but that's because the school run (that affects the morning peak) is usually done by 1600.
Vehicle scheduling is one of those "how hard can it be" sorts of things that, in reality, is much more difficult. That said, if people are continually vexed at the lateness of the service, they can always get the TC to investigate should they get no joy from the operator.