CS 25 says this.
AMC 25.111(b)
Take-off Path
1 Rotation speed, VR, is intended to be the speed at which the pilot initiates action to raise the nose gear off the ground, during the acceleration to V2; consequently, the take-off path determination, in accordance with CS 25.111 (a) and (b), should assume that pilot action to raise the nose gear off the ground will not be initiated until the speed VR has been reached.
2 The time between lift-off and the initiation of gear retraction during take-off distance
demonstrations should not be less than that necessary to establish an indicated positive rate of climb plus one second. For the purposes of flight manual expansion, the average demonstrated time delay between lift-off and initiation of gear retraction may be assumed; however, this value should not be less than 3 seconds.
Last edited by FE Hoppy; 3rd Feb 2006 at 12:26.