You need to complete at least one year after being issued the RP(residence permit) itself, not one year from the time you joined the company. There are companies who applied for the RP only after three months of your initial employment, hence if that's the case, your tenure with the company could be more than one year before you can be under a differenct sponsor. You can however ask for a "letter of lend" from your present employer. It's a type of NOC where your current sponsor allows you to work with other companies but still under their sponsorship since you still do not qualify to be under a new sponsor.