I know the pubs are not authoritative, but they have good info regarding schedule C vs schedule E, or something else. Pubs. 527 and 334 are good ones to look at. Don't see anything referencing 7 days or less. From Pub. 527:
Which Forms To Use
The basic form for reporting residential rental income and expenses is Schedule E (Form 1040). However, don’t use that schedule to report a not-for-profit activity. See Not Rented for Profit, in chapter 4. There also are other rental situations in which forms other than Schedule E would be used.
Schedule E (Form 1040)
If you rent buildings, rooms, or apartments, and provide basic services such as heat and light, trash collection, etc., you normally report your rental income and expenses on Schedule E, Part I.
List your total income, expenses, and depreciation for each rental property. Be sure to enter the number of fair rental and personal use days on line 2.
If you have more than three rental or royalty properties, complete and attach as many Schedules E as are needed to list the proper-ties. Complete lines 1 and 2 for each property. However, fill in lines 23a through 26 on only one Schedule E.
On Schedule E, page 1, line 18, enter the depreciation you are claiming for each property. To find out if you need to attach Form 4562, see Form 4562, later.
If you have a loss from your rental real estate activity, you also may need to complete one or both of the following forms.
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Form 6198, At-Risk Limitations. See At-Risk Rules, later. Also see Pub. 925.
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Form 8582, Passive Activity Loss Limitations. See Passive Activity Limits, later.
Page 2 of Schedule E is used to report in-come or loss from partnerships, S corporations, estates, trusts, and real estate mortgage investment conduits. If you need to use page 2 of Schedule E, be sure to use page 2 of the same Schedule E you used to enter your rental activity on page 1. Also, include the amount from line 26 (Part I) in the “Total income or (loss)” on line 41 (Part V).
Form 4562. You must complete and attach Form 4562 for rental activities only if you are claiming:
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Depreciation, including the special depreciation allowance, on property placed in service during 2018;
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Depreciation on listed property (such as a car), regardless of when it was placed in service; or
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Any other car expenses, including the standard mileage rate or lease expenses. Otherwise, figure your depreciation on your own worksheet. You don’t have to attach these computations to your return, but you should keep them in your records for future reference.
See Pub. 946 for information on preparing Form 4562.
Schedule C (Form 1040), Profit or Loss From Business
Generally, Schedule C is used when you provide substantial services in conjunction with the property or the rental is part of a trade or business as a real estate dealer.
Providing substantial services. If you provide substantial services that are primarily for your tenant's convenience, such as regular cleaning, changing linen, or maid service, you report your rental income and expenses on Schedule C (Form 1040), Profit or Loss From Business, or Schedule C-EZ (Form 1040), Net Profit From Business. Use Form 1065, U.S. Return of Partnership Income, if your rental activity is a partnership (including a partnership with your spouse unless it is a qualified joint venture). Substantial services don’t include the furnishing of heat and light, cleaning of public areas, trash collection, etc. For more information, see Pub. 334, Tax Guide for Small Business. Also, you may have to pay self-employment tax on your rental income using Schedule SE (Form 1040), Self-Employment Tax. For a discussion of “substantial services,” see Real Estate Rents in Pub. 334, chapter 5.