I am wondering if the following might be of help. Bathsheba Day, daughter of Edward Day, game keeper, married in 1845.
In 1851, she said she was aged 28 [hence born c 1823] in Yarlington in Somerset.
Hence, it this is the same Edward Day, Bathsheba might be a sister to Edward DD and could have been born in Somerset - before the family came to Hampshire??
08 Oct 1845; Marriage - Edward TIZARD of full age; Bachelor of Weymouth Sailor; Father: William Stevens TIZARD Pilot;
& Bathsheba DAY of full age; Spinster of Melcombe Regis; Father: Edward DAY Gamekeeper; John Orton TIZARD & Jane TIZARD; T. Burn Anstis; By Licence
Marriage, Wyke Regis, Dorset.
1851 Census of Weymouth - District 4a - HO107/1857, 321-p2
9; Hope Quay No9;
Edward TIZARD; Head; Mar; 32; m; Pilot; Dorset Weymouth;
Bathsheba TIZARD; Wife; Mar; 28; f; Pilots Wife; Somerset Yarlington;
Mary Ann TIZARD; Daur; Sch; 5; f; Scholar; Dorset Weymouth;
Edward L TIZARD; Son; 2; m; Dorset Weymouth;
[Hence Bathsheba born c1823?]
Baptisms
June 01 1852 Bathsheba TIZARD; Edward & Bathsheba of Weymouth; Pilot
February 20 1859 Jane Florina TIZARD; Edward & Bathsheba of Weymouth; Mariner
The only Day/Selborne connection that I can find for the 1820s is:-
1829 9 Sep., Susan Day of Selborne, aged 20, buried.
No baptism found for her in Selborne in c1809.
Yours Jane