The transitional period which allowed employers to delay automatically enrolling their workers into a pension scheme ended on 30 September 2017.
An employer could only use transitional delay to delay automatically enrolling some or all of their eligible jobholders on its staging date. An employers staging date is set in law and is the date the automatic enrolment duties apply to them.
If your employer used transitional delay to delay automatically enrolling you into the LGPS this would have remained in place until 30 September 2017. If you were still an eligible jobholder on 1 October 2017 your employer should have automatically enrolled you into the LGPS from that date (unless you had opted out more than 12 months before 1 October 2017, in which case the duty to automatically you enrol you does not apply).
You can elect to join the LGPS at any time whether you are an eligible jobholder or not. If you wish to opt-in to the LGPS contact your LGPS Pension Fund for an application form.