Representing Central Gauteng Athletics at the National Road Running Championships in Gqeberha on Saturday, Sosibo was the first South African home in the 21.1km race.
She finished second overall in 1:12:38, just two seconds behind Namibia's Lavina Haitope, who claimed victory in 1:12:36.
There was little time to celebrate her breakthrough achievement, because less than 24 hours later, the 28-year-old travelled to Durban to compete for Boxer Running Club in the Spar Women's 10km Challenge.
Despite racing on tired legs, the Johannesburg-based athlete, coached by veteran Michael Seme, fought hard to finish fourth in a personal best time of 32:16.
Speaking to SABC Sport, Sosibo said the scheduling made it impossible for elite athletes to perform at their best.
"The calendar really messed up our weekend. It affected our performances in both races. Running a half-marathon one day and then a 10km the next is not ideal for elite athletes," said Sosibo.
"I want to appeal to ASA to give us at least a week between the national championships and another major race.
“That would allow us enough time to recover. This arrangement did not work for me, and I hope it doesn't happen again."
The KwaZulu-Natal-born runner admitted the demanding schedule eventually caught up with her, despite making a strong start in Durban.
"My body reminded me that I had raced a hard 21km the previous day. I couldn't recover properly. My flight from Gqeberha was at 4pm, I arrived in Durban around 6pm, only got to sleep late, and had to wake up at 5am for the race."
"I normally sleep for about 10 hours before a race. In Gqeberha, I raced hard against the Ethiopian athletes, and that took a lot out of me. Even so, I'm happy that I still managed to run a personal best over 10km."