Cash ISA 
This is still an early look at this code, things can and do change quite frequently at Monzo. So wih you pinch of salt at the ready… Here’s some code surrounding the ISAs 
<string name="pot_class_subtitles_flexible_savings">"Cash ISA option available
Withdraw the next working day
Earn up to %s interest"</string>
<string name="pot_class_subtitles_flexible_savings_isa_only">"Tax-free cash ISA
Withdraw the next working day
Earn up to %s interest"</string>
<string name="pot_creation_fixed_savings_estimation_message">Since this flow was started before midnight and we’re now into another day, our estimations may have changed. Please start the flow again for accurate estimations.</string>
<string name="pot_creation_fixed_savings_estimation_title">Estimates may have changed</string>
<string name="pot_term_length_confirm_negative">Change length</string>
<string name="pot_term_length_confirm_positive">Confirm</string>
<string name="pot_term_length_confirm_title">Confirm term length</string>
<string name="pot_term_length_deposit_description">If you deposited</string>
<string name="pot_term_length_interest_amount">%s%% interest on this term length</string>
<string name="pot_term_length_number_of_months">Number of months</string>
<string name="pot_term_length_title">Select term length</string>
<string name="pot_term_length_total_interest">Total interest earned: %s</string>
<string name="pot_term_length_total_savings">Your total savings</string>
What does all of this mean? 
It means that Monzo ISAs might still take a day to get your funds returned 
(I could be very wrong though).
It also looks like there’s been a great deal of expansion surrounding fixed ISAs (this would be in addition to a regular Cash ISA) 
mentions of term lengths & a the use of variable numbers show that there will, more than likely, be better interest rates the longer you lock your funds away for 