In any case where engineering or design standards or city policies or rules establish conditions that cannot be met in a specific situation without removal of a protected, heritage or ancestral tree, the City Council shall determine what specific adverse effect would result from waiver or modification of such standard, policy, rule or application thereof, to the extent necessary to save the tree. If the City Council determines that there is no serious and imminent adverse effect, the standard, policy or rule may be modified or waived. In circumstances involving regulations under the authority of the Board of Adjustment, the Board of Adjustment will have determination and modification authority. All determinations required to be made under this chapter shall be made before the expiration of 30 working days from the date of the application for approval for tree removal, except in cases requiring Board of Adjustment review which will have 60 working days for approval of tree removal.