Richard,
Apologies as you will have raced by the time you read this reply (I hope things went well!); nevertheless, hopefully others can benefit and you’ll be able to take the following to your next event.
For a VK or similarly moderate duration (45-75min) endurance event, it’s key to make sure your anaerobic system is online. Your ability to produce and effectively metabolize lactate is a key component to performing well and not blowing up halfway through such a rigorous effort, and the warmup is the first step in getting everything firing well.
I like to think about such warmups from the context of a Formula 1 race car. You don’t just roll one of those souped-up babies out of the garage and onto the track then punch the accelerator through the firewall to 150mph – if you did, the engine would explode and you’d be a sad puddle of goo on the side of the road (or trail, so to speak). Instead, you need to start with warmth: easy movement for 15-20min, building up to and slightly above your Aerobic Threshold to warm the muscles and get blood moving, without developing any lactate by-product. For a VK i prefer to do this part on flat terrain so I can be jogging or lightly running. Following this you can begin to work through your Z2 and low Z3 with some moderate repeats, now on specific uphill terrain. I typically will do 2x 3-4min (1-2 min rest) and aim to finish each repeat at or slightly above my anaerobic threshold heart rate. Finally, I’ll do one or two 1 minute repeats at a race-pace effort, on specific terrain (the course itself, if possible) with only 1 minute recovery.
Following that last interval I will jog very easy back down the hill to the start area, ensuring that I have about 10 minutes remaining before start. To your above question, 10 minutes is certainly not too long; you want sufficient time for your body to re-metabolize the lactate you produced during the final portions of the warmup; this will ensure that your metabolism is engaged and “online” for the effort to come. This time window also allows you to get into race clothes, grab some water and stretch a few minutes before the gun.
For the tl:dr types, here’s the warmup routine in bullet form:
15-20 minutes easy running, building up to AeT
2x 3-4 minutes building from AeT to AnT, with 1 minute walk/jogging rest
2x 1 minute at AnT+ (race effort) on specific terrain, with 1 minute recovery
— Allow 10 minutes between end of warmup and start of race —
Good luck!