nraas

I don't want to marry him or have babies with him. I just want woohoo.

Is there any way to mess with Woohooer to get this?

When I first got the game, my witch sim was successful after hitting him with a love charm. Since, I found the future world to be boring, I never tried again.

The Time Traveler is part of the Service Pool, on default SP Settings "Friendship: Allow" is set "False" in their particular Caste "Service Population".
You may want to set it to True in the particular Caste so it can engage into a friendly relationship between your Sim and even invite him over to your house when he's not doing anything in your world.

Or after you interacted with the time portal the first time and before you completed the challenge, you can pause the game, click on the time travel and change these settings on him in SP> Sim Options>
1. Friendship Allow> True
2. (not sure but check) Romance Allow> True (if False within parentheses set it on true)
3. Pregnancy: Allow Participation> True

See if that works for you. Woohooer is more of a global thing that counts for all Sims within in their restrictions, SP is where you need to look.

Non-ITF player here, but I thought there were some sort of really bad issues that can develop if one tries to make babies with the Time Traveler. Not that Echo was asking for that, only mentioning it because it was included in the SP options to check out.

I blocked this because it causes too many problems.

Blocked woohoo or just pregnancy? Woohoo is just an interaction, right?

Both. He's a weird hybrid service and role Sim. Unfortunately I don't recall the specific problem years later but from what I recall he breaks when interrupted somehow.

Ah. So it really can't be done. Bummer.

You'll just have to accept that you cant get a piece of him :p Chain_Reaction has "chained up" the woohoo. i never thought about involving the time traveler in our stories... now I am thinking about how we could hack around the blockage... like maybe we can ensorcel him and then we can control him for awhile?
Yeah, I do testy things and break the game

Well after looking at the code in the game I'm afraid not
<CodeVersion>EP11</CodeVersion>
<RoleType>TimeTraveler</RoleType>
<CanBeEnsorceled>FALSE</CanBeEnsorceled>