Hello! A-320 a/c. In my company SOP the positive rate of climb is when radio alt, vertical rate and pressure alt are going up.
Let's imagine a litle bit. You've just airbone so the first signe of the positive rate that you can see is radio alt changes (one second of time). Second, the most obvious, sign is VSI changes (another second). Third, the pressure alt changes, it is one more second. Next we confirm:"posituve climb" and PF order:"Gear up". Then PNF moves the gear leather up.
Totally we have ay least 5 seconds from lifting up to the begining of gear up preses. With the average speed is equal to ~500 f/m we will be at 41' above ground. so you don't need to worry about to early gear retraction.
Con respecto!