The basic rule is that you may donate only twice in any 7-day period and you must wait at least 48 hours between donations. So, if you first donated on Tuesday then you can't donate again until Thursday or later. Assuming you donate on those two days, then your next (third) donation must wait until the following Tuesday...after which the sequence repeats, from there.
Andrea answered. If you donate plasma any day of the week the next time would be two days later. So Monday and Wednesday, Tuesday and Thursday and so on. You cannot donate at more than one place.
If Tuesday is the first day you donated, you would be a new donor on Tuesday
Thanks! Your answer is awaiting moderation.