The answer depends on whether you are talking ITA, USTA, or ITF. They all have different rules. But this 10 min thing mentioned above is not correct.
I will assume you are talking USTA. It is complicated depending on a lot of factors, the most important being whether or not a trainer is available. If a trainer is available, once the trainer reaches the player they have a maximum of 5 minutes of which a max for treatment is 3 minutes. If trainer takes 4 min for evaluation, then the treatment that may be received is only 1 minute. You may take 1 medical timeout per injury, but you can’t be treated for an injury that previously treated. For example, if you sprain your ankle, you can take a MTO. Later you hurt your back, you can take an MTO. Later you re-injure your ankle. You now either have to play on with no MTO allowed or retire. There a lot of nuances to MTOs so I suggest you go online and check out “Friend at Court” for all the rules. The rles still applies if there is no trainer. You have a max treatment time of 3 min to treat yourself. Of course, time is allowed to go get ice, etc. It is a lot more complicated than this but that is the gist.