After the defeat in Tampere, the Red Guards began a slow retreat eastwards. As the German army seized Helsinki, the White Army shifted the military focus to Vyborg area, where 18,500 Whites advanced against 15,000 defending Reds. General Mannerheim's war plan had been revised as a result of the Battle for Tampere, a civilian, industrial town. He aimed to avoid new, complex city combat in Vyborg, an old military fortress. The Jäger detachments tried to tie down and destroy the Red force outside the town. The Whites were able to cut the Reds' connection to Petrograd and weaken the troops on the Karelian Isthmus on 20-26 April, but the decisive blow remained to be dealt in Vyborg. The final attack began on late 27 April with a heavy Jäger artillery barrage. The Reds' defence collapsed gradually, and eventually the Whites conquered Patterinmäki—the Reds' symbolic last stand of the 1918 uprising—in the early hours of 29 April 1918. In total, 400 Whites died, and 500-600 Reds perished and 12,000-15,000 were captured.
Question: How many days was the time span where the Whites were able to cut the Reds' connection to Petrograd and weaken the troops on the Karelian Isthmus?
Answer: 6