The answer differs depending on which type of virtual events are you doing.
For Virtual Challenges, yes.
Virtual Challenges are completed by accumulating distances to meet the distance goal. You can do multiple challenges at the same time. Just keep mind that submitted distances will be counted toward all active challenges simultaneously.
For Virtual Races, no.
Virtual Races are completed in one go. You need to finish the current Virtual Race before you enter another one.
💡Tips: Registration code never expire. You can hold on to your code(s) until you are ready.