Just now spoken with the home office at below no.
Visas, settlement and asylum - Contact the Croydon Contact Centre about asylum, settlement, extending your stay in the UK, work and study visas
Telephone: 0300 123 2241
Monday to Thursday, 9am to 4:45pm
Friday, 9am to 4:30pm
https://ukvi-international.faq-help.com/
The person interacted me told, ILR eligibility starts from 5 years from the day your visa is valid/starts and you have entered within 90 days from this start date. you can apply 28 days before this 5 years completion. if your circumstance within this criteria adjust your appointment in the available slots without paying extra money ( if you have premium appointments paid before 18th mar 16). Any views from the experienced here..?