Does a person's failure to repent from procrastinating repentance, after disbelieving in Allah and then declaring the Shahada and entering Islam, make him a disbeliever?

Failing to repent due to procrastination is not disbelief (kufr), but rather a sin that necessitates repentance. General repentance, which encompasses all sins, is sufficient for it. Initiating repentance from a sin is an immediate obligation (fardh 'ala al-fawr), and delaying it is a disobedience that necessitates another repentance for the delay itself. Nothing saves one from this except a general repentance that includes sins the servant knows and those he does not know, because what he does not know is more numerous. Indeed, the Prophet, peace and blessings be upon him, used to seek Allah's forgiveness for every sin he knew and every sin he did not know.