How long should I Carnbonate

I’m still new to kegging and have looked at many of the carbonation threads on HBT, including the Carbonation pressure chart

http://www.kegerators.com/articles/carbonation-table-pressure-chart.php

and the Carbonation chart from Bobby M https://www.homebrewtalk.com/f35/keg-force-carbing-methods-illustrated-73328/

I decided I wanted a CO2 volume of approx 2.5. My keg temperature is 40 deg, so I set my regulator to 13psi for a slow carbonation rate.

I know this question has been asked before but I am still a little confused because what the Carbonation pressure chart does not show is how long it takes for the beer to be fully carbonated.

I do not mind waiting, but at the moment I wait a week try the beer, wait a few more days and try it again etc until it reaches the carbonation that I like.

Is there a way of calculating when my beer is ready to drink? Thanks

The green line in Bobby's chart shows 2-3 weeks for complete carbonation. I set mine at 10 and start drinking in 7-10 days. You could speed things up a bit by setting it at 25 for a couple/few days and gently rock it for several minutes each day being careful not to over carb.
Set it and forget works the best though. Set it at your working psi and wait a couple of weeks.

My last two batches were carbed @ 40 degrees and 14 PSI, and both had good carbonation in 5-7 days. No rocking or shaking, just set it and forget it. My PSI was slightly higher than yours, but I don't imagine 1 PSI would make much difference. My LHBS told me to expect ~10 days at this pressure/temp, but I've not had to wait that long so far for good beer.

As for calculating the estimated time, I have no clue. I've never been more scientific than just sampling every few days.

Thanks for the replies. I have been sampling every few days and it gets better every time. I will try a slightly higher PSI for my next brew and see if it makes much difference time wise. I like the set and forget method, but need to schedule my brewing better so that I do not run out of beer as I have at the moment.

I do 25-28 psi at 42*F for about 56 hours then bleed and pressurize to 12 for about 3 days. I avoid the keg until 7 or 8 days to let it all settle out. First half pint is junky, but clears well around day 14.