Setting Short Date Time property with server C# method

Hello,

I am trying to set a Date property that has a Pattern of Short Date Time with the below code. Even though it is yyyy-MM-dd hh:mm:ss tt in the string it is still saying that it is not formatted correctly? Below is the code and the error. Thank you for your help!

Innovator inn = this.getInnovator();
Item controlledItem = this.apply("GetControlledItem");
if (controlledItem.isError()) {
return inn.newError("smc_TechInquiry_Notifications: Retrive Workflow: Unexpected error: " + controlledItem.getErrorString());
}

string time = DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss tt");

string idofitem = controlledItem.getID();
Item item2 = inn.getItemById("smc_TechInquiry",idofitem);
item2.setProperty("_timestamp_assigned",time);

item2.setAction("edit");
item2.apply();

return this;