Soft top change took mechanic 10 hours??

Estimated was 4-5 hours and max 8 hours and if anything he would let me know if there are difficulties.

Now he sends me astronomical bill because he works per hour and it took 2 guys 10 hours.

Is it even possible for professionals to do it in 10 hours?? Can I use “they didn’t call me to warn me” as a possibility to lower the price because it is cosmic