I think you can hold your altcoin in your wallet for a long time even for two years or longer. Its totally up to you. The amount of your token will remain the same but the value of it after two years or so, we'll never know. It might increase is value, it might decrease, or the worst case scenario, it might no longer exist. Also you will need gas to trade it.The gas fee after two years might also increase. I you think the token has a lot of potential, then keep it as long as you want, but if not, then trade it as soon as possible.
In most cases it could be considered safe and I say majority because there will be exceptions,what if,for example,the developers think about changing the coin or token doing an exchange or swap putting a grace period of a certain time,which once finished will not do more exchanges that could give a headache to the owner of the wallet that for one reason or another He/She forgot to make the change on time,that's why you should pay special attention to that kind of detail before thinking about hold altcoins for years in a wallet.