Hi,
Just had a quick look and I believe you can keep the cash in there for some time as: -
I got this from Hargreaves Lansdown ISA FAQ
Just had a quick look and I believe you can keep the cash in there for some time as: -
How long can I hold cash within a Stocks & Shares ISA?
HM Revenue and Customs regulations do not set a timescale, however, they do stipulate that you must hold the cash in the account with the intention to reinvest at some point in the future.
I got this from Hargreaves Lansdown ISA FAQ