Can I give somene an insincere "I forgive you" if I see the matter is pressing to them? All the while I will keep working on fully forgiving them, but I know they can not manage to wait that much.

Listen, this is a very delicate situation, and you need to understand something fundamental about forgiveness. When someone presses you for forgiveness and you're not ready, you have to be honest about where you are in the process. If you say "I forgive you" with your mouth but you don't mean it in your heart, that's lying. You cannot just say the words while still keeping all that anger and hatred filed away in your heart. Either you forgive or you don't forgive - it can't be both. The Baal Shem Tov teaches that the way you forgive others is how Hashem forgives you in Shamayim. If you're a fake forgiver, saying the words but not meaning them, then in Shamayim they'll treat you the same way. Now, here's what you need to know: There is a process to get to genuine forgiveness, and it starts with action even before your heart is fully there. You can take action to at least make it look like you forgive, to at least make it look like you're not offended by it. You say "I forgive you" even though in your heart you're not completely there yet. Why? Because your words will eventually lead your actions to change your heart. When you keep saying "I forgive you," your neshamah starts to appreciate the spiritual level you're reaching, and this process softens your heart, breaks the klipah covering it, and eventually leads you to genuinely forgive the person. But you cannot say "I forgive you" to someone while simultaneously planning to bring it up later or keeping it in your file cabinet with a red stripe on it to use when needed. That's not forgiveness - that's deception. If you accept their apology and say everything is good, then it has to be over. You can't tell them it's okay and then remind them of it fifteen years later during a fight. When you tell someone you forgive them, you're telling them it's okay for them to move on with their life. If it's not really okay, then you need to continue discussing it with them until it actually is resolved, or you need to honestly tell them you're not ready to forgive yet. The bottom line is this: Start with the action of saying "I forgive you" and work on making it genuine in your heart through prayer, through thinking about what they did and choosing to let it go, and through recognizing that holding onto anger only destroys you, not them. But don't be one of these people who makes public statements about forgiving everyone while still hating them in your heart. Do it privately, write their names down, pray for them, and work on forgiving them wholeheartedly. That's real teshuva on your part, and that's what Hashem wants from you.