Does the share price always rise after a SPAC announce merger with a target company?

Does the share price always rise after a SPAC (special purpose acquisition company) announces merger with a target company?

I feel the only purpose of a SPAC is to merge with a target company and bring the target company to public.

So, I assume the share price of the SPAC will always rise following the merger announcement.

However, does the announcement always happen after 4:00pm EST?

If this is true, then it is still difficult for retail investors to buy the shares immediately following the announcement?