× I hope you have a fantastic summer and that you can visit us early.
√ I hope you have a fantastic summer and that you can visit us soon.
Early means ‘near the beginning of a period of time’: ‘I’ll see you early in the morning.’ ‘We got up very early yesterday.’ [=early in the morning]
Soon means ‘a short time later than now’: ‘I’ll see you soon’. ‘I hope you get well soon.’
Compare:
- They will be here early. [=early tomorrow in the morning, for example]
- They will be here soon. [=some time later than now, I don’t know exactly when]