What to do on ARRIVAL of destination re: combining/shortening

[Yusuf Khan]

السلام عليكم،

If one is following the opinion of the 4 days = traveling...
1) WHEN do the 4 days start? IMMEDIATELY when one arrives, or the next day (I've heard that the day one arrives it still counts as traveling time or something? and then counts 96 hours?)

2) Now upon arrival of the destination one is traveling to, can they combine (or was it shorten too?) upon the day they arrived? meaning like say I arrive in X at 'Asr time of X... I can now combine my zuhr and 'asr....and then later I can combine my maghrib and 'isha (for that day)?
THEN after those days (if I'm staying more than 4 days), I have to pray fully and normally?

(I know I asked it in a confusing way, but I don't know how else to ask it haha جزاك الله خيرا)