While you can enter the UK at any time during the 33 months, if you leave it more than 3 months and 28 days, your future FLR(M) visa may expire before you can qualify to apply for ILR.
If that happens you would have to apply for an extra FLR(M), at a cost of probably over £1000 by then, to make up the difference in the time between your visa expiring and you being able to qualify for ILR.
So, it's up to you whether you would be willing to apply for an extra visa in 5 years' time because you left it more than 3 months and 28 days.
If you don't want to have to shell out all that extra money for it, then you should enter the UK within 3 months and 28 days of Feb 6th.