[Will_f]

If I'm going to wear the watch frequently, I get it regulated after the first month or two. My watch maker charges 30-40 bucks depending on the watch, but totally worth it. The comments about isochronism (consistency independent of position and temperature) are true though. Some movements just vary too much to be worth regulating tighter than 5-10s per day. Also, if your watch has a free sprung movement it's going to cost more to regulate, but it's likely to be very accurate.

 

[Will_f]

My seiko monster's accuracy is between +20s per day when the watch is fully wound (when i wear it all day long, plus 5-6 minutes of swirling it!) and -5s with normal use (8-10 hours).
Is something wrong with the isochronism? I would like it to be more consistent...

Sounds like the indexing pins that control the active length of the hair spring have a little too much play. As the spring winds down, the amplitude of the balance wheel is less and the hairspring isn't touching the index pins as much, allowing a longer effective spring length and slower oscillation. A competent watch maker can certainly fix it, though it might cost more than you're comfortable spending on an inexpensive watch.