Yes. Depending on your personal circumstances and financial goals, this can be a very sensible thing to do – for example if you want to commit to different amounts over different durations, or are using this product to save up for something other than retirement (such as to fund future education expenses for your children, or anything else). Having multiple accounts can be a very effective way of separating your different savings objectives, and it also means that if for whatever reason you want to make a withdrawal or reduce the amount you save each month, you can do so on one of your accounts without affecting the guaranteed minimum future value on your other accounts.
It is also common for people to gradually earn more money as they get more experienced and reputable at whatever it is they do to earn money, and is sensible to save more money when you find yourself earning more money, so yes you can start another pension plan at any time you choose.