AFAIK we are not allowed to use more than one stadium in a Premier League season. So it's either Wembley all season or new stadium all season. I'm not going back to Wembley for regular league matches.
From the PL Rulebook
Ground Registration
K.5. Each Club shall register its Stadium with the Board and must play all matches in the competitions listed in Rule L.9 for which it is the Home Club at the Stadium.
No Club shall remove to another Stadium (either on a permanent or temporary basis) without first obtaining the written consent of the Board, in accordance with Rule K.6, below.
K.6. In considering whether to give any such consent, the Board shall have regard to all the circumstances of the case (including, but not limited to, the factors set out in this Rule K.6) and shall not consent unless reasonably satisfied that such consent:
K.6.1. would be consistent with the objects of the League as set out in the
Memorandum;
K.6.2. would be appropriate having in mind the relationship (if any) between the locality with which by its name or otherwise the applicant Club is traditionally associated and that in which such Club proposes to establish its Stadium;
K.6.3. would not to any material extent adversely affect such Club’s Officials, Players, supporters, shareholders, sponsors and others having an interest in its activities;
K.6.4. would not have a material adverse effect on Visiting Clubs;
K.6.5. would not to any material extent adversely affect Clubs (or Football
League clubs) having their registered grounds in the immediate vicinity of
the proposed location; and
K.6.6. would enhance the reputation of the League and promote the game of association football generally
So we can use more than one. As long as there is consent from the Premier League. Timing of when it occurs is not mentioned in the rules.