Should I raise risks immediately when I see one or should I try to resolve the risk first and then raise it. How long should I try before raising one.
Communication and transparency are key principles in managing a project so stakeholders know what is going on and you maintain trust with them. So early and often communication messages to stakeholders should be a critical success factor for you.
That said, there is a very real psychological component when it comes to risks that you need to manage. What people want to hear and what they need to hear are often times--too often--not the same thing. Intellectually, stakeholders know they need to know and understand the threats jeopardizing their project for which they are spending money. Emotionally, they want to hear that everything is running perfectly, success is a guarantee, issues are few and uneventful, and risks don't exist. In a very real way, we all thrive in this illusion. We reward our employees who maintain that illusion for us, by calling them 'can-do', positive employees and discriminating them against the alwaysnegativeboatrockingtroublemakers.
As the PM, you likely want the same thing when you're dealing with your team, and your team wants to come across like optimistic, can-do people so they will naturally hide their threats. So your challenge is to break through your own desires of wanting that illusion with your team and then communicating that to your stakeholders while you desperately want to hide those threats. And then you need to manage their adverse reaction of bringing up what they need to but don't want to hear.
However, their reaction is very real and can materially affect how they engage in your project in a negative way. Raising your risks--the right thing to do--can cause you more trouble, exacerbating your impacts, more than the risk itself. Therefore, there are benefits, real benefits, in choosing not to disclose and mitigating under the radar. That choice is not free of costs and risks so it becomes a trade-off analysis you need to do but you need to do it and it will result in some of those risks being treated stealthily. Perhaps it's an 80/20 rule, where only 20% going hidden. I don't really know. That's for you to decide.
One thing you should know is that, as a project manager, one of your main goals is to raise, mitigate or resolve risks. But you must definitely differentiate between the risks that concern your board (thus you should not keep it for yourself nor deal with them alone), and the risks that concern you (kind of risks that only need your position and abilities). So make the balance, and if you believe that the risk is of the first type, don't hesitate and raise it.