Not HL. But i can give you mt experience of the Freetrade side. Whole things was less than 3 weeks (Vanguard). Once the pervious provider had processed the transfer and Freetrade had received it my shares were available almost immediately (same day, couple of hours) on Freetrade. Same for cash, it was collected a few days later, once the cash was transferred it was available again almost immediately.
Overall much better experience than other ive had where everything will disappear from one broker then reappear in the new broker a number of days later.
It wasn’t blocked for me, but it meant i had two ISAs open at the same time in the same tax year, I couldn’t use the Freetrade one as my previous one was still active and funded within the tax year. It seems a grey area with the rules (what can you using during a transfer) but i dont believe the freetrade one it technically supposed to be used while you have an existing active isa still open.