Meaning of "sitting by the hour"

Question

Mrs. Pritchard was to accompany me on the train that would take me on the overnight trip from Nairobi to Mombasa, where I would board the ship. For three days I had resisted wearing Valerie’s clothes, but now I had to put them on. Mrs. Pritchard herself had altered the clothes to fit me, sitting by the hour, tears dropping onto the silks and linens as she took in seams and shortened hems. Seeing her unhappiness, my dislike began to melt away.

I checked the meaning of "by the hour" on the net as every hour, but in this context I think its meaning is something different.

Does it mean:

1. She sat fitting the clothes for an hour?

or

2. She sat fitting the clothes for hours?

Source: Listening for Lions by Gloria Whelan

Answer 1

The correct meaning is option 2.

Look it up and you will see from context the persons are sitting hour after hour

Sunday was his only day off, and I recall his sitting by the hour at a desk in the living room decorating stamp album pages with carefully rendered designs.

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Our debates continued endlessly. On long walks or sitting by the hour over cups of coffee, he would enthusiastically attempt to “prove” that true music was born with Wagner

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by the hour​/​from hour to hour continuously, or all the time
The fire grew bigger by the hour.

^{macmillandictionary}