I'm sorry to hear about your son's situation. They can hold him initially for thirty days:
Sec. 15. COMMITMENT TO AWAIT REQUISITION; BAIL. If from the examination before the judge or magistrate it appears that the person held is the person charged with having committed the crime alleged and except in cases arising under Section 6, that he has fled from justice, the judge or magistrate must, by warrant reciting the accusation, commit him to the county jail for such time not exceeding thirty days and specified in the warrant, as will enable the arrest of the accused to be made under a warrant of the Governor on a requisition of the Executive Authority of the State having jurisdiction of the offense, unless the accused give bail as provided in the next section, or until he shall be legally discharged.
However, a judge can extend that initial thirty days by sixty more days:
Sec. 17. EXTENSION OF TIME OF COMMITMENT; ADJOURNMENT. If the accused is not arrested under warrant of the Governor by the expiration of the time specified in the warrant or bond, a judge or magistrate may discharge him or may recommit him for a further period not to exceed sixty days, or a judge or magistrate may again take bail for his appearance and surrender, as provided in Section 16, but within a period not to exceed sixty days after the date of such new bond.
It is unlikely for a violation of probation that a judge will extend the time in jail to await a pickup by Oklahoma. They do not generally extend unless there is a very good reason why Oklahoma couldn't pick him up during the initial 30 days. So it is likely that they won't hold him more than 30 days, and possibly even less if Oklahoma tells Texas that they don't intend to extradite before the 30 days is up.