Arum's Top Rank and Mayweather's representatives at Golden Boy Promotions agreed to the mediation in an effort to resolve their dispute over the methods and frequency of drug testing for the bout, which will be held at the MGM Grand Garden in Las Vegas if a compromise is reached.
Although both fighters have agreed to extensive urine testing, Mayweather has demanded random blood testing as well. Pacquiao has balked at unlimited blood testing, instead proposing two blood tests before the fight and another immediately afterward.
Pacquiao also complicated the negotiations by filing a lawsuit last week alleging Mayweather and most of his camp's key players defamed him by falsely accusing him of using performance-enhancing drugs.
Neither side would say whether more mediation will be held Wednesday, but the length of Tuesday's meeting appeared to be a positive development for the potential fight. If little progress could be made, the session likely would have been scrapped early, with the sport's top two fighters moving on to replacement bouts instead of meeting in what's expected to be the richest fight in boxing history.
After impressive pay-per-view numbers in their most recent bouts last year, both fighters stand to make more than $25 million in their welterweight meeting. Except for drug testing, the camps have settled every significant detail of the fight, according to Arum and Golden Boy CEO Richard Schaefer.
If the fight falls through, Pacquiao is expected to attempt to win a title in a record eighth weight division with a bout against 154-pound champion Yuri Foreman in Las Vegas on March 20, while Mayweather could fight former 140-pound champion Paulie Malignaggi at the MGM Grand on March 13.
Boxing's two most prominent promotional companies have appeared before Weinstein in the past, including a session in 2007 in which they resolved the promotional rights to Pacquiao, who had deals with both companies at one point.