Antonio,
To create a sick leave under time account, see the steps below
1. Go to configuration-->time account types--> add row-->sick leave --> add category, unit, creation, recurrence, valid from and valid to--> below you will see bookable from six months later( as this is may be your probation period)-->bookable to --> check limit--> minimum balance limit-->valid from and valid to and save.
2. Go to time account rules--> sick leave-->assign code and time account rule--> go below-->annual entitlement-->accrual rule-->add accrual date, posting type, accrual quantity--> then go period end rules--> set up period end rules and save.
Regards,
Emeka