Will the duration of heat-shock affect transformation efficiency? "

There is little difference between 15~45 seconds of heat-shock. For most Elite™ strains, 15~35 seconds of heat-shock is optimal for transformation of plasmid < 6 Kb. 45 second heat shock is not optimal for plasmid < 6 Kb (may decrease 1.2~2.5 times, strain dependent) but is optimal for > 6 Kb plasmid.