One long drive from Venice to Split

For your safety, I hope you will be reasonably well rested before starting the long drive immediately after getting off the plane? Jet lag has caused some people problems in driving. Especially at night and on unfamiliar roads.

yes. no worries about Jet lag. We're coming from Europe. and we'll make sure to rest well before :)

Oh good, you aren't coming from across the Pond.

You'll need to make sure with the rental company that you can take the car to Croatia. It's not necessarily the case (most French rentals wouldn't allow it by default for instance).
Border crossings are easy, for your route the Best place to cross is Starod/Pasjak, open twenty-four hours, but do stay alert on the 2-lane road across Slovenia, it is a little bit winding.

Landing at 6pm means it will be 7/7.30 by the time you are ready to depart with your hire car. I have just looked at Google Maps which suggests that the quickest route would take over 7 hours and the roads will be quieter now (1am) than at 7/8 pm plus Google always underestimates by about a third. Assume it will take 8-9 hours without stopping plus any delays at the border crossing. You need a vignette to drive in Slovenia, assuming your hire company permits this.

Even if you are arriving from within Europe, you aren’t going to be alert enough for this drive. Why arrive in Split at 4am? You will be wiped out for a few days. Spend the night in Venice or close to it and undertake the drive in daylight when refreshed and make the most of the scenery.

Thanks everyone for your feedback. I'll consider it but anyone knows how good are the roads in this area?
Is it a pleasant night drive and not too dangerous?
Thanks!

There is a not-so-pleasant section of 2-lane road through Slovenia which is unpleasant, but at least it means you do NOT need a Slovenia vignette for the journey. Coming from Trieste, you just cross the country on E61 in less than 60 minutes when traffic is light. Once in Croatia, you're soon back on divided highways.
With two drivers, the journey is feasible, but again, provided it is allowed by the car rental company!
It is also nicer by day; if you drive by day you could make it nicer (but longer) by taking the coast highway (E65) from Rijeka to Maslenica near Zadar.
Some days, Volotea flies Venice to Split in the early morning: with your dates, have you looked at that alternative? You'd spend a night at Venice Aiport and rent a car in Split instead.

Once you get into Croatia, the rest of the drive can be mainly on expressways or it can involve some secondary roads. For example, I've driven the E65 along the coast between Senj and Rijeka. It's well maintained but far from an expressway. It may be better to drive east to the E71 which reconnects with the E65 near Zadar. I wouldn't label a night drive from Venice to Split "pleasant" (more like grueling), but it's probably not any more dangerous than driving for several hours at night on any major highway.

When are you doing this drive? Between November and March I definitely wouldn't risk it as you may encounter some very strong winds and slippery conditions. The road is otherwise fine, a divided highway up until Trieste and from about Rijeka onwards. The section through Slovenia is a two-lane road that is wide enough but winding, although you may encounter deer if driving after dark.

In any case I would spend the night somewhere along the way and then continue the following morning. It's a very long drive and the scenery is fantastic, it would be a shame to miss it by driving at night.