As the question says. Not sure what the consequences may be in terms of legal and effect on career and networking down the line.
You know what sticks out more than a short interlude at company A? Being unemployed for half a year.
Even worse if you don't already have a written offer from company B.
Also, you might like job A way more than job B. There's nothing to lose from accepting job offer A and then after a few weeks decide if you want to stay, want to do a personal time-out until B starts, or if you wait until the last possible day to hand in your notice and go on to job B.
The probation period on a job works both ways, it's not only you that has to impress a company, it's also the other way around. If you already have job B lined up, you're in a great position to check out company A.
Is it ok to accept A, starting working and quit before B start date?
There are lots of details missing from your post that would help us give a more precise answer, but in general terms no, it's not ok.
Here are some reasons why it would not be ok or why it could be harmful or backfire on you:
- You will most likely burn all bridges will company A by quitting shortly after starting for a job. Even more if you knew this all along and just took A "in the meantime".
- Accepting offer from A may also mean you could have a notice period to hand when considering quitting, so you would have to consider that for your timings to be right. That assumes that you care about serving your notice period. If you don't serve that would be very unprofessional again.
- Accepting offer from A may also bring an NDA or Non-compete agreement that you should sign. This could be problematic if this conflicts with your offer from B, and you would be in professional and legal trouble if you decide to ignore it.
- This hop from A to B will show up in a background check if they want to look for such things, so be ready to explain about it for a long time to come when seeking employment in the future ("why did you had a job in A for such a few time and then went to B?")
- You never know what the future has prepared for you. If there is such thing as "work karma" it could come and bite you in the future if you use A in such way (for example, what if someone from the interview panel has to interview you again? ouch).
Like I said, much details are missing from your post to help you better. Assuming you are currently employed, and that you prefer B over A, I would suggest you take B, politely decline and thank for offer A, keep doing your current job, hand your notice period sometime near next summer, server it and move on.
It's fine, as long as you are careful with thing like notice periods.
It's not that uncommon for people to start work and then get a better offer only a few months later. If it's significantly better then it's unreasonable to expect them to stick with the first offer, which is demonstrably below market rate.
Sometimes people quit after a few months because they realize the job just isn't for them. And sometimes the company lets them go for the same reason. Most jobs designate the first few months as a probationary period with minimal notice and no invitation to things like the company pension scheme, for those reasons.
Just be sure you give the required amount of notice. Don't say anything else if they ask why, beyond that you have been given a better opportunity.
I think the question would benefit from a frame change:
If you were employed by company A and had only been working for them for 4 months would you then accept a job offer from company B?
The answer will vary according to the exact situation but most people would only choose to move if there is a strong tangible benefit to doing so.
For what its worth I don't think that company B values you very highly if they are insisting on a 6 month wait before you can work there.
Do you think company would want to hire you, knowing you'll only be working for them for 3 months?
If the answer is "yes", then tell them upfront you can only join for a few months, and it's perfectly fine to do this. You and they will both get something good out of it.
If the answer is "no", and you're not telling them upfront, then by doing this you are being dishonest about your intentions, and doing something you know the other party would not be interested in if they your plans, and that should never be okay.